OpenSSL: SSLKEYLOGFILE support

[users/jgh/exim.git] / doc / doc-txt / NewStuff

New Features in Exim
--------------------

This file contains descriptions of new features that have been added to Exim.
Before a formal release, there may be quite a lot of detail so that people can
test from the snapshots or the Git before the documentation is updated. Once
the documentation is updated, this file is reduced to a short list.

Version 4.93
------------

 1. An "external" authenticator, per RFC 4422 Appendix A.

 2. A JSON lookup type, and JSON variants of the forall/any expansion conditions.

 3. Variables $tls_in_cipher_std, $tls_out_cipher_std giving the RFC names
    for ciphersuites.

 4. Log_selectors "msg_id" (on by default) and "msg_id_created".

 5. A case_insensitive option for verify=not_blind.

 6. EXPERIMENTAL_TLS_RESUME optional build feature.  See the experimental.spec
    file.

 7. A main option exim_version to override the version Exim
    reports in verious places ($exim_version, $version_number).

 8. Expansion operator ${sha2_N:} for N=256, 384, 512.

 9. Router variables, $r_... settable from router options and usable in routers
    and transports.

10. The spf lookup now supports IPv6.

11. Main options for DKIM verify to filter hash and key types.

12. Under GnuTLS, with TLS1.3, support for full-chain OCSP stapling.

13. Dual-certificate stacks on servers now support OCSP stapling, under OpenSSL.

14: An smtp:ehlo transport event, for observability of the remote offered features.

15: Support under OpenSSL for writing NSS-style key files for packet-capture
    decode.  The environment variable SSLKEYLOGFILE is used; if an absolute path
    it must indicate a file under the spool directory; if relative the the spool
    directory is prepended.  Works on the server side only.  Support under 
    GnuTLS was already there, being done purely by the library (server side
    only, and exim must be run as root).


Version 4.92
--------------

 1. ${l_header:<name>} and ${l_h:<name>} expansion items, giving a colon-sep
    list when there are multiple headers having a given name.  This matters
    when individual headers are wrapped onto multiple lines; with previous
    facilities hard to parse.

 2. The ${readsocket } expansion item now takes a "tls" option, doing the
    obvious thing.

 3. EXPERIMENTAL_REQUIRETLS and EXPERIMENTAL_PIPE_CONNECT optional build
    features.  See the experimental.spec file.

 4. If built with SUPPORT_I18N a "utf8_downconvert" option on the smtp transport.

 5. A "pipelining" log_selector.

 6. Builtin macros for supported log_selector and openssl_options values.

 7. JSON variants of the ${extract } expansion item.

 8. A "noutf8" debug option, for disabling the UTF-8 characters in debug output.

 9. TCP Fast Open support on MacOS.

Version 4.91
--------------

 1. Dual-certificate stacks on servers now support OCSP stapling, under GnuTLS
    version 3.5.6 or later.

 2. DANE is now supported under GnuTLS version 3.0.0 or later.  Both GnuTLS and
    OpenSSL versions are moved to mainline support from Experimental.
    New SMTP transport option "dane_require_tls_ciphers".

 3. Feature macros for the compiled-in set of malware scanner interfaces.

 4. SPF support is promoted from Experimental to mainline status.  The template
    src/EDITME makefile does not enable its inclusion.

 5. Logging control for DKIM verification.  The existing DKIM log line is
    controlled by a "dkim_verbose" selector which is _not_ enabled by default.
    A new tag "DKIM=<domain>" is added to <= lines by default, controlled by
    a "dkim" log_selector.

 6. Receive duration on <= lines, under a new log_selector "receive_time".

 7. Options "ipv4_only" and "ipv4_prefer" on the dnslookup router and on
    routing rules in the manualroute router.

 8. Expansion item ${sha3:<string>} / ${sha3_<N>:<string>} now also supported
    under OpenSSL version 1.1.1 or later.

 9. DKIM operations can now use the Ed25519 algorithm in addition to RSA, under
    GnuTLS 3.6.0 or OpenSSL 1.1.1 or later.

10. Builtin feature-macros _CRYPTO_HASH_SHA3 and _CRYPTO_SIGN_ED25519, library
    version dependent.

11. "exim -bP macro <name>" returns caller-usable status.

12. Expansion item ${authresults {<machine>}} for creating an
    Authentication-Results: header.

13. EXPERIMENTAL_ARC.  See the experimental.spec file.
    See also new util/renew-opendmarc-tlds.sh script for use with DMARC/ARC.

14: A dane:fail event, intended to facilitate reporting.

15. "Lightweight" support for Redis Cluster. Requires redis_servers list to
    contain all the servers in the cluster, all of which must be reachable from
    the running exim instance. If the cluster has master/slave replication, the
    list must contain all the master and slave servers.

16. Add an option to the Avast scanner interface: "pass_unscanned". This
    allows to treat unscanned files as clean. Files may be unscanned for
    several reasons: decompression bombs, broken archives.


Version 4.90
------------

 1. PKG_CONFIG_PATH can now be set in Local/Makefile;
    wildcards will be expanded, values are collapsed.

 2. The ${readsocket } expansion now takes an option to not shutdown the
    connection after sending the query string.  The default remains to do so.

 3. An smtp transport option "hosts_noproxy_tls" to control whether multiple
    deliveries on a single TCP connection can maintain a TLS connection
    open.  By default disabled for all hosts, doing so saves the cost of
    making new TLS sessions, at the cost of having to proxy the data via
    another process.  Logging is also affected.

 4. A malware connection type for the FPSCAND protocol.

 5. An option for recipient verify callouts to hold the connection open for
    further recipients and for delivery.

 6. The reproducible build $SOURCE_DATE_EPOCH environment variable is now
    supported.

 7. Optionally, an alternate format for spool data-files which matches the
    wire format - meaning more efficient reception and transmission (at the
    cost of difficulty with standard Unix tools).  Only used for messages
    received using the ESMTP CHUNKING option, and when a new main-section
    option "spool_wireformat" (false by default) is set.

 8. New main configuration option "commandline_checks_require_admin" to
    restrict who can use various introspection options.

 9. New option modifier "no_check" for quota and quota_filecount
    appendfile transport.

10. Variable $smtp_command_history returning a comma-sep list of recent
    SMTP commands.

11. Millisecond timetamps in logs, on log_selector "millisec".  Also affects
    log elements QT, DT and D, and timstamps in debug output.

12. TCP Fast Open logging.  As a server, logs when the SMTP banner was sent
    while still in SYN_RECV state; as a client logs when the connection
    is opened with a TFO cookie.

13. DKIM support for multiple signing, by domain and/or key-selector.
    DKIM support for multiple hashes, and for alternate-identity tags.
    Builtin macro with default list of signed headers.
    Better syntax for specifying oversigning.
    The DKIM ACL can override verification status, and status is visible in
    the data ACL.

14. Exipick understands -C|--config for an alternative Exim
    configuration file.

15. TCP Fast Open used, with data-on-SYN, for client SMTP via SOCKS5 proxy,
    for ${readsocket } expansions, and for ClamAV.

16. The "-be" expansion test mode now supports macros.  Macros are expanded
    in test lines, and new macros can be defined.

17. Support for server-side dual-certificate-stacks (eg. RSA + ECDSA).


Version 4.89
------------

 1. Allow relative config file names for ".include"

 2. A main-section config option "debug_store" to control the checks on
    variable locations during store-reset.  Normally false but can be enabled
    when a memory corruption issue is suspected on a production system.


Version 4.88
------------

 1. The new perl_taintmode option allows to run the embedded perl
    interpreter in taint mode.

 2. New log_selector: dnssec, adds a "DS" tag to acceptance and delivery lines.

 3. Speculative debugging, via a "kill" option to the "control=debug" ACL
    modifier.

 4. New expansion item ${sha3:<string>} / ${sha3_<N>:<string>}.
    N can be 224, 256 (default), 384, 512.
    With GnuTLS 3.5.0 or later, only.

 5. Facility for named queues:  A command-line argument can specify
    the queue name for a queue operation, and an ACL modifier can set
    the queue to be used for a message.  A $queue_name variable gives
    visibility.

 6. New expansion operators base32/base32d.

 7. The CHUNKING ESMTP extension from RFC 3030.  May give some slight
    performance increase and network load decrease.  Main config option
    chunking_advertise_hosts, and smtp transport option hosts_try_chunking
    for control.

 8. LMDB lookup support, as Experimental. Patch supplied by Andrew Colin Kissa.

 9. Expansion operator escape8bit, like escape but not touching newline etc..

10. Feature macros, generated from compile options.  All start with "_HAVE_"
    and go on with some roughly recognisable name.  Driver macros, for
    router, transport and authentication drivers; names starting with "_DRIVER_".
    Option macros, for each configuration-file option; all start with "_OPT_".
    Use the "-bP macros" command-line option to see what is present.

11. Integer values for options can take a "G" multiplier.

12. defer=pass option for the ACL control cutthrough_delivery, to reflect 4xx
    returns from the target back to the initiator, rather than spooling the
    message.

13. New built-in constants available for tls_dhparam and default changed.

14. If built with EXPERIMENTAL_QUEUEFILE, a queuefile transport, for writing
    out copies of the message spool files for use by 3rd-party scanners.

15. A new option on the smtp transport, hosts_try_fastopen.  If the system
    supports it (on Linux it must be enabled in the kernel by the sysadmin)
    try to use RFC 7413 "TCP Fast Open".  No data is sent on the SYN segment
    but it permits a peer that also supports the facility to send its SMTP
    banner immediately after the SYN,ACK segment rather then waiting for
    another ACK - so saving up to one roundtrip time.  Because it requires
    previous communication with the peer (we save a cookie from it) this
    will only become active on frequently-contacted destinations.

16. A new syslog_pid option to suppress PID duplication in syslog lines.


Version 4.87
------------

 1. The ACL conditions regex and mime_regex now capture substrings
    into numeric variables $regex1 to 9, like the "match" expansion condition.

 2. New $callout_address variable records the address used for a spam=,
    malware= or verify= callout.

 3. Transports now take a "max_parallel" option, to limit concurrency.

 4. Expansion operators ${ipv6norm:<string>} and ${ipv6denorm:<string>}.
    The latter expands to a 8-element colon-sep set of hex digits including
    leading zeroes. A trailing ipv4-style dotted-decimal set is converted
    to hex.  Pure ipv4 addresses are converted to IPv4-mapped IPv6.
    The former operator strips leading zeroes and collapses the longest
    set of 0-groups to a double-colon.

 5. New "-bP config" support, to dump the effective configuration.

 6. New $dkim_key_length variable.

 7. New base64d and base64 expansion items (the existing str2b64 being a
    synonym of the latter).  Add support in base64 for certificates.

 8. New main configuration option "bounce_return_linesize_limit" to
    avoid oversize bodies in bounces. The default value matches RFC
    limits.

 9. New $initial_cwd expansion variable.


Version 4.86
------------

 1. Support for using the system standard CA bundle.

 2. New expansion items $config_file, $config_dir, containing the file
    and directory name of the main configuration file. Also $exim_version.

 3. New "malware=" support for Avast.

 4. New "spam=" variant option for Rspamd.

 5. Assorted options on malware= and spam= scanners.

 6. A command-line option to write a comment into the logfile.

 7. If built with EXPERIMENTAL_SOCKS feature enabled, the smtp transport can
    be configured to make connections via socks5 proxies.

 8. If built with EXPERIMENTAL_INTERNATIONAL, support is included for
    the transmission of UTF-8 envelope addresses.

 9. If built with EXPERIMENTAL_INTERNATIONAL, an expansion item for a commonly
    used encoding of Maildir folder names.

10. A logging option for slow DNS lookups.

11. New ${env {<variable>}} expansion.

12. A non-SMTP authenticator using information from TLS client certificates.

13. Main option "tls_eccurve" for selecting an Elliptic Curve for TLS.
    Patch originally by Wolfgang Breyha.

14. Main option "dns_trust_aa" for trusting your local nameserver at the
    same level as DNSSEC.


Version 4.85
------------

 1. If built with EXPERIMENTAL_DANE feature enabled, Exim will follow the
    DANE SMTP draft to assess a secure chain of trust of the certificate
    used to establish the TLS connection based on a TLSA record in the
    domain of the sender.

 2. The EXPERIMENTAL_TPDA feature has been renamed to EXPERIMENTAL_EVENT
    and several new events have been created. The reason is because it has
    been expanded beyond just firing events during the transport phase. Any
    existing TPDA transport options will have to be rewritten to use a new
    $event_name expansion variable in a condition. Refer to the
    experimental-spec.txt for details and examples.

 3. The EXPERIMENTAL_CERTNAMES features is an enhancement to verify that
    server certs used for TLS match the result of the MX lookup. It does
    not use the same mechanism as DANE.


Version 4.84
------------


Version 4.83
------------

 1. If built with the EXPERIMENTAL_PROXY feature enabled, Exim can be
    configured to expect an initial header from a proxy that will make the
    actual external source IP:host be used in exim instead of the IP of the
    proxy that is connecting to it.

 2. New verify option header_names_ascii, which will check to make sure
    there are no non-ASCII characters in header names.  Exim itself handles
    those non-ASCII characters, but downstream apps may not, so Exim can
    detect and reject if those characters are present.

 3. New expansion operator ${utf8clean:string} to replace malformed UTF8
    codepoints with valid ones.

 4. New malware type "sock".  Talks over a Unix or TCP socket, sending one
    command line and matching a regex against the return data for trigger
    and a second regex to extract malware_name.  The mail spoolfile name can
    be included in the command line.

 5. The smtp transport now supports options "tls_verify_hosts" and
    "tls_try_verify_hosts".  If either is set the certificate verification
    is split from the encryption operation. The default remains that a failed
    verification cancels the encryption.

 6. New SERVERS override of default ldap server list.  In the ACLs, an ldap
    lookup can now set a list of servers to use that is different from the
    default list.

 7. New command-line option -C for exiqgrep to specify alternate exim.conf
    file when searching the queue.

 8. OCSP now supports GnuTLS also, if you have version 3.1.3 or later of that.

 9. Support for DNSSEC on outbound connections.

10. New variables "tls_(in,out)_(our,peer)cert" and expansion item
    "certextract" to extract fields from them. Hash operators md5 and sha1
    work over them for generating fingerprints, and a new sha256 operator
    for them added.

11. PRDR is now supported dy default.

12. OCSP stapling is now supported by default.

13. If built with the EXPERIMENTAL_DSN feature enabled, Exim will output
    Delivery Status Notification messages in MIME format, and negotiate
    DSN features per RFC 3461.


Version 4.82
------------

 1. New command-line option -bI:sieve will list all supported sieve extensions
    of this Exim build on standard output, one per line.
    ManageSieve (RFC 5804) providers managing scripts for use by Exim should
    query this to establish the correct list to include in the protocol's
    SIEVE capability line.

 2. If the -n option is combined with the -bP option, then the name of an
    emitted option is not output, only the value (if visible to you).
    For instance, "exim -n -bP pid_file_path" should just emit a pathname
    followed by a newline, and no other text.

 3. When built with SUPPORT_TLS and USE_GNUTLS, the SMTP transport driver now
    has a "tls_dh_min_bits" option, to set the minimum acceptable number of
    bits in the Diffie-Hellman prime offered by a server (in DH ciphersuites)
    acceptable for security.  (Option accepted but ignored if using OpenSSL).
    Defaults to 1024, the old value.  May be lowered only to 512, or raised as
    far as you like.  Raising this may hinder TLS interoperability with other
    sites and is not currently recommended.  Lowering this will permit you to
    establish a TLS session which is not as secure as you might like.

    Unless you really know what you are doing, leave it alone.

 4. If not built with DISABLE_DNSSEC, Exim now has the main option
    dns_dnssec_ok; if set to 1 then Exim will initialise the resolver library
    to send the DO flag to your recursive resolver.  If you have a recursive
    resolver, which can set the Authenticated Data (AD) flag in results, Exim
    can now detect this.  Exim does not perform validation itself, instead
    relying upon a trusted path to the resolver.

    Current status: work-in-progress; $sender_host_dnssec variable added.

 5. DSCP support for outbound connections: on a transport using the smtp driver,
    set "dscp = ef", for instance, to cause the connections to have the relevant
    DSCP (IPv4 TOS or IPv6 TCLASS) value in the header.

    Similarly for inbound connections, there is a new control modifier, dscp,
    so "warn control = dscp/ef" in the connect ACL, or after authentication.

    Supported values depend upon system libraries.  "exim -bI:dscp" to list the
    ones Exim knows of.  You can also set a raw number 0..0x3F.

 6. The -G command-line flag is no longer ignored; it is now equivalent to an
    ACL setting "control = suppress_local_fixups".  The -L command-line flag
    is now accepted and forces use of syslog, with the provided tag as the
    process name.  A few other flags used by Sendmail are now accepted and
    ignored.

 7. New cutthrough routing feature.  Requested by a "control = cutthrough_delivery"
    ACL modifier; works for single-recipient mails which are received on and
    deliverable via SMTP.  Using the connection made for a recipient verify,
    if requested before the verify, or a new one made for the purpose while
    the inbound connection is still active.  The bulk of the mail item is copied
    direct from the inbound socket to the outbound (as well as the spool file).
    When the source notifies the end of data, the data acceptance by the destination
    is negotiated before the acceptance is sent to the source.  If the destination
    does not accept the mail item, for example due to content-scanning, the item
    is not accepted from the source and therefore there is no need to generate
    a bounce mail.  This is of benefit when providing a secondary-MX service.
    The downside is that delays are under the control of the ultimate destination
    system not your own.

    The Received-by: header on items delivered by cutthrough is generated
    early in reception rather than at the end; this will affect any timestamp
    included.  The log line showing delivery is recorded before that showing
    reception; it uses a new ">>" tag instead of "=>".

    To support the feature, verify-callout connections can now use ESMTP and TLS.
    The usual smtp transport options are honoured, plus a (new, default everything)
    hosts_verify_avoid_tls.

    New variable families named tls_in_cipher, tls_out_cipher etc. are introduced
    for specific access to the information for each connection.  The old names
    are present for now but deprecated.

    Not yet supported: IGNOREQUOTA, SIZE, PIPELINING.

 8. New expansion operators ${listnamed:name} to get the content of a named list
    and ${listcount:string} to count the items in a list.

 9. New global option "gnutls_allow_auto_pkcs11", defaults false.  The GnuTLS
    rewrite in 4.80 combines with GnuTLS 2.12.0 or later, to autoload PKCS11
    modules.  For some situations this is desirable, but we expect admin in
    those situations to know they want the feature.  More commonly, it means
    that GUI user modules get loaded and are broken by the setuid Exim being
    unable to access files specified in environment variables and passed
    through, thus breakage.  So we explicitly inhibit the PKCS11 initialisation
    unless this new option is set.

    Some older OS's with earlier versions of GnuTLS might not have pkcs11 ability,
    so have also added a build option which can be used to build Exim with GnuTLS
    but without trying to use any kind of PKCS11 support.  Uncomment this in the
    Local/Makefile:

    AVOID_GNUTLS_PKCS11=yes

10. The "acl = name" condition on an ACL now supports optional arguments.
    New expansion item "${acl {name}{arg}...}" and expansion condition
    "acl {{name}{arg}...}" are added.  In all cases up to nine arguments
    can be used, appearing in $acl_arg1 to $acl_arg9 for the called ACL.
    Variable $acl_narg contains the number of arguments.  If the ACL sets
    a "message =" value this becomes the result of the expansion item,
    or the value of $value for the expansion condition.  If the ACL returns
    accept the expansion condition is true; if reject, false.  A defer
    return results in a forced fail.

11. Routers and transports can now have multiple headers_add and headers_remove
    option lines.  The concatenated list is used.

12. New ACL modifier "remove_header" can remove headers before message gets
    handled by routers/transports.

13. New dnsdb lookup pseudo-type "a+".  A sequence of "a6" (if configured),
    "aaaa" and "a" lookups is done and the full set of results returned.

14. New expansion variable $headers_added with content from ACL add_header
    modifier (but not yet added to message).

15. New 8bitmime status logging option for received messages.  Log field "M8S".

16. New authenticated_sender logging option, adding to log field "A".

17. New expansion variables $router_name and $transport_name.  Useful
    particularly for debug_print as -bt command-line option does not
    require privilege whereas -d does.

18. If built with EXPERIMENTAL_PRDR, per-recipient data responses per a
    proposed extension to SMTP from Eric Hall.

19. The pipe transport has gained the force_command option, to allow
    decorating commands from user .forward pipe aliases with prefix
    wrappers, for instance.

20. Callout connections can now AUTH; the same controls as normal delivery
    connections apply.

21. Support for DMARC, using opendmarc libs, can be enabled. It adds new
    options: dmarc_forensic_sender, dmarc_history_file, and dmarc_tld_file.
    It adds new expansion variables $dmarc_ar_header, $dmarc_status,
    $dmarc_status_text, and $dmarc_used_domain.  It adds a new acl modifier
    dmarc_status.  It adds new control flags dmarc_disable_verify and
    dmarc_enable_forensic. The default for the dmarc_tld_file option is
    "/etc/exim/opendmarc.tlds" and can be changed via EDITME.

22. Add expansion variable $authenticated_fail_id, which is the username
    provided to the authentication method which failed.  It is available
    for use in subsequent ACL processing (typically quit or notquit ACLs).

23. New ACL modifier "udpsend" can construct a UDP packet to send to a given
    UDP host and port.

24. New ${hexquote:..string..} expansion operator converts non-printable
    characters in the string to \xNN form.

25. Experimental TPDA (Transport Post Delivery Action) function added.
    Patch provided by Axel Rau.

26. Experimental Redis lookup added. Patch provided by Warren Baker.


Version 4.80
------------

 1. New authenticator driver, "gsasl".  Server-only (at present).
    This is a SASL interface, licensed under GPL, which can be found at
    http://www.gnu.org/software/gsasl/.
    This system does not provide sources of data for authentication, so
    careful use needs to be made of the conditions in Exim.

 2. New authenticator driver, "heimdal_gssapi".  Server-only.
    A replacement for using cyrus_sasl with Heimdal, now that $KRB5_KTNAME
    is no longer honoured for setuid programs by Heimdal.  Use the
    "server_keytab" option to point to the keytab.

 3. The "pkg-config" system can now be used when building Exim to reference
    cflags and library information for lookups and authenticators, rather
    than having to update "CFLAGS", "AUTH_LIBS", "LOOKUP_INCLUDE" and
    "LOOKUP_LIBS" directly.  Similarly for handling the TLS library support
    without adjusting "TLS_INCLUDE" and "TLS_LIBS".

    In addition, setting PCRE_CONFIG=yes will query the pcre-config tool to
    find the headers and libraries for PCRE.

 4. New expansion variable $tls_bits.

 5. New lookup type, "dbmjz".  Key is an Exim list, the elements of which will
    be joined together with ASCII NUL characters to construct the key to pass
    into the DBM library.  Can be used with gsasl to access sasldb2 files as
    used by Cyrus SASL.

 6. OpenSSL now supports TLS1.1 and TLS1.2 with OpenSSL 1.0.1.

    Avoid release 1.0.1a if you can.  Note that the default value of
    "openssl_options" is no longer "+dont_insert_empty_fragments", as that
    increased susceptibility to attack.  This may still have interoperability
    implications for very old clients (see version 4.31 change 37) but
    administrators can choose to make the trade-off themselves and restore
    compatibility at the cost of session security.

 7. Use of the new expansion variable $tls_sni in the main configuration option
    tls_certificate will cause Exim to re-expand the option, if the client
    sends the TLS Server Name Indication extension, to permit choosing a
    different certificate; tls_privatekey will also be re-expanded.  You must
    still set these options to expand to valid files when $tls_sni is not set.

    The SMTP Transport has gained the option tls_sni, which will set a hostname
    for outbound TLS sessions, and set $tls_sni too.

    A new log_selector, +tls_sni, has been added, to log received SNI values
    for Exim as a server.

 8. The existing "accept_8bitmime" option now defaults to true.  This means
    that Exim is deliberately not strictly RFC compliant.  We're following
    Dan Bernstein's advice in http://cr.yp.to/smtp/8bitmime.html by default.
    Those who disagree, or know that they are talking to mail servers that,
    even today, are not 8-bit clean, need to turn off this option.

 9. Exim can now be started with -bw (with an optional timeout, given as
    -bw<timespec>).  With this, stdin at startup is a socket that is
    already listening for connections.  This has a more modern name of
    "socket activation", but forcing the activated socket to fd 0.  We're
    interested in adding more support for modern variants.

10. ${eval } now uses 64-bit values on supporting platforms.  A new "G" suffix
    for numbers indicates multiplication by 1024^3.

11. The GnuTLS support has been revamped; the three options gnutls_require_kx,
    gnutls_require_mac & gnutls_require_protocols are no longer supported.
    tls_require_ciphers is now parsed by gnutls_priority_init(3) as a priority
    string, documentation for which is at:
    http://www.gnutls.org/manual/html_node/Priority-Strings.html

    SNI support has been added to Exim's GnuTLS integration too.

    For sufficiently recent GnuTLS libraries, ${randint:..} will now use
    gnutls_rnd(), asking for GNUTLS_RND_NONCE level randomness.

12. With OpenSSL, if built with EXPERIMENTAL_OCSP, a new option tls_ocsp_file
    is now available.  If the contents of the file are valid, then Exim will
    send that back in response to a TLS status request; this is OCSP Stapling.
    Exim will not maintain the contents of the file in any way: administrators
    are responsible for ensuring that it is up-to-date.

    See "experimental-spec.txt" for more details.

13. ${lookup dnsdb{ }} supports now SPF record types. They are handled
    identically to TXT record lookups.

14. New expansion variable $tod_epoch_l for higher-precision time.

15. New global option tls_dh_max_bits, defaulting to current value of NSS
    hard-coded limit of DH ephemeral bits, to fix interop problems caused by
    GnuTLS 2.12 library recommending a bit count higher than NSS supports.

16. tls_dhparam now used by both OpenSSL and GnuTLS, can be path or identifier.
    Option can now be a path or an identifier for a standard prime.
    If unset, we use the DH prime from section 2.2 of RFC 5114, "ike23".
    Set to "historic" to get the old GnuTLS behaviour of auto-generated DH
    primes.

17. SSLv2 now disabled by default in OpenSSL.  (Never supported by GnuTLS).
    Use "openssl_options -no_sslv2" to re-enable support, if your OpenSSL
    install was not built with OPENSSL_NO_SSL2 ("no-ssl2").


Version 4.77
------------

 1. New options for the ratelimit ACL condition: /count= and /unique=.
    The /noupdate option has been replaced by a /readonly option.

 2. The SMTP transport's protocol option may now be set to "smtps", to
    use SSL-on-connect outbound.

 3. New variable $av_failed, set true if the AV scanner deferred; ie, when
    there is a problem talking to the AV scanner, or the AV scanner running.

 4. New expansion conditions, "inlist" and "inlisti", which take simple lists
    and check if the search item is a member of the list.  This does not
    support named lists, but does subject the list part to string expansion.

 5. Unless the new EXPAND_LISTMATCH_RHS build option is set when Exim was
    built, Exim no longer performs string expansion on the second string of
    the match_* expansion conditions: "match_address", "match_domain",
    "match_ip" & "match_local_part".  Named lists can still be used.


Version 4.76
------------

 1. The global option "dns_use_edns0" may be set to coerce EDNS0 usage on
    or off in the resolver library.


Version 4.75
------------

 1. In addition to the existing LDAP and LDAP/SSL ("ldaps") support, there
    is now LDAP/TLS support, given sufficiently modern OpenLDAP client
    libraries.  The following global options have been added in support of
    this: ldap_ca_cert_dir, ldap_ca_cert_file, ldap_cert_file, ldap_cert_key,
    ldap_cipher_suite, ldap_require_cert, ldap_start_tls.

 2. The pipe transport now takes a boolean option, "freeze_signal", default
    false.  When true, if the external delivery command exits on a signal then
    Exim will freeze the message in the queue, instead of generating a bounce.

 3. Log filenames may now use %M as an escape, instead of %D (still available).
    The %M pattern expands to yyyymm, providing month-level resolution.

 4. The $message_linecount variable is now updated for the maildir_tag option,
    in the same way as $message_size, to reflect the real number of lines,
    including any header additions or removals from transport.

 5. When contacting a pool of SpamAssassin servers configured in spamd_address,
    Exim now selects entries randomly, to better scale in a cluster setup.


Version 4.74
------------

 1. SECURITY FIX: privilege escalation flaw fixed. On Linux (and only Linux)
    the flaw permitted the Exim run-time user to cause root to append to
    arbitrary files of the attacker's choosing, with the content based
    on content supplied by the attacker.

 2. Exim now supports loading some lookup types at run-time, using your
    platform's dlopen() functionality.  This has limited platform support
    and the intention is not to support every variant, it's limited to
    dlopen().  This permits the main Exim binary to not be linked against
    all the libraries needed for all the lookup types.


Version 4.73
------------

 NOTE: this version is not guaranteed backwards-compatible, please read the
       items below carefully

 1. A new main configuration option, "openssl_options", is available if Exim
    is built with SSL support provided by OpenSSL.  The option allows
    administrators to specify OpenSSL options to be used on connections;
    typically this is to set bug compatibility features which the OpenSSL
    developers have not enabled by default.  There may be security
    consequences for certain options, so these should not be changed
    frivolously.

 2. A new pipe transport option, "permit_coredumps", may help with problem
    diagnosis in some scenarios.  Note that Exim is typically installed as
    a setuid binary, which on most OSes will inhibit coredumps by default,
    so that safety mechanism would have to be overridden for this option to
    be able to take effect.

 3. ClamAV 0.95 is now required for ClamAV support in Exim, unless
    Local/Makefile sets: WITH_OLD_CLAMAV_STREAM=yes
    Note that this switches Exim to use a new API ("INSTREAM") and a future
    release of ClamAV will remove support for the old API ("STREAM").

    The av_scanner option, when set to "clamd", now takes an optional third
    part, "local", which causes Exim to pass a filename to ClamAV instead of
    the file content.  This is the same behaviour as when clamd is pointed at
    a Unix-domain socket.  For example:

      av_scanner = clamd:192.0.2.3 1234:local

    ClamAV's ExtendedDetectionInfo response format is now handled.

 4. There is now a -bmalware option, restricted to admin users.  This option
    takes one parameter, a filename, and scans that file with Exim's
    malware-scanning framework.  This is intended purely as a debugging aid
    to ensure that Exim's scanning is working, not to replace other tools.
    Note that the ACL framework is not invoked, so if av_scanner references
    ACL variables without a fallback then this will fail.

 5. There is a new expansion operator, "reverse_ip", which will reverse IP
    addresses; IPv4 into dotted quad, IPv6 into dotted nibble.  Examples:

      ${reverse_ip:192.0.2.4}
       -> 4.2.0.192
      ${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3}
       -> 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2

 6. There is a new ACL control called "debug", to enable debug logging.
    This allows selective logging of certain incoming transactions within
    production environments, with some care.  It takes two options, "tag"
    and "opts"; "tag" is included in the filename of the log and "opts"
    is used as per the -d<options> command-line option.  Examples, which
    don't all make sense in all contexts:

      control = debug
      control = debug/tag=.$sender_host_address
      control = debug/opts=+expand+acl
      control = debug/tag=.$message_exim_id/opts=+expand

 7. It has always been implicit in the design and the documentation that
    "the Exim user" is not root.  src/EDITME said that using root was
    "very strongly discouraged".  This is not enough to keep people from
    shooting themselves in the foot in days when many don't configure Exim
    themselves but via package build managers.  The security consequences of
    running various bits of network code are severe if there should be bugs in
    them.  As such, the Exim user may no longer be root.  If configured
    statically, Exim will refuse to build.  If configured as ref:user then Exim
    will exit shortly after start-up.  If you must shoot yourself in the foot,
    then henceforth you will have to maintain your own local patches to strip
    the safeties off.

 8. There is a new expansion condition, bool_lax{}.  Where bool{} uses the ACL
    condition logic to determine truth/failure and will fail to expand many
    strings, bool_lax{} uses the router condition logic, where most strings
    do evaluate true.
    Note: bool{00} is false, bool_lax{00} is true.

 9. Routers now support multiple "condition" tests.

10. There is now a runtime configuration option "tcp_wrappers_daemon_name".
    Setting this allows an admin to define which entry in the tcpwrappers
    config file will be used to control access to the daemon.  This option
    is only available when Exim is built with USE_TCP_WRAPPERS.  The
    default value is set at build time using the TCP_WRAPPERS_DAEMON_NAME
    build option.

11. [POSSIBLE CONFIG BREAKAGE] The default value for system_filter_user is now
    the Exim run-time user, instead of root.

12. [POSSIBLE CONFIG BREAKAGE] ALT_CONFIG_ROOT_ONLY is no longer optional and
    is forced on.  This is mitigated by the new build option
    TRUSTED_CONFIG_LIST which defines a list of configuration files which
    are trusted; one per line. If a config file is owned by root and matches
    a pathname in the list, then it may be invoked by the Exim build-time
    user without Exim relinquishing root privileges.

13. [POSSIBLE CONFIG BREAKAGE] The Exim user is no longer automatically
    trusted to supply -D<Macro[=Value]> overrides on the command-line.  Going
    forward, we recommend using TRUSTED_CONFIG_LIST with shim configs that
    include the main config.  As a transition mechanism, we are temporarily
    providing a work-around: the new build option WHITELIST_D_MACROS provides
    a colon-separated list of macro names which may be overridden by the Exim
    run-time user.  The values of these macros are constrained to the regex
    ^[A-Za-z0-9_/.-]*$ (which explicitly does allow for empty values).


Version 4.72
------------

 1. TWO SECURITY FIXES: one relating to mail-spools which are globally
    writable, the other to locking of MBX folders (not mbox).

 2. MySQL stored procedures are now supported.

 3. The dkim_domain transport option is now a list, not a single string, and
    messages will be signed for each element in the list (discarding
    duplicates).

 4. The 4.70 release unexpectedly changed the behaviour of dnsdb TXT lookups
    in the presence of multiple character strings within the RR. Prior to 4.70,
    only the first string would be returned.  The dnsdb lookup now, by default,
    preserves the pre-4.70 semantics, but also now takes an extended output
    separator specification.  The separator can be followed by a semicolon, to
    concatenate the individual text strings together with no join character,
    or by a comma and a second separator character, in which case the text
    strings within a TXT record are joined on that second character.
    Administrators are reminded that DNS provides no ordering guarantees
    between multiple records in an RRset.  For example:

      foo.example.  IN TXT "a" "b" "c"
      foo.example.  IN TXT "d" "e" "f"

      ${lookup dnsdb{>/ txt=foo.example}}   -> "a/d"
      ${lookup dnsdb{>/; txt=foo.example}}  -> "def/abc"
      ${lookup dnsdb{>/,+ txt=foo.example}} -> "a+b+c/d+e+f"


Version 4.70 / 4.71
-------------------

 1. Native DKIM support without an external library.
    (Note that if no action to prevent it is taken, a straight upgrade will
    result in DKIM verification of all signed incoming emails.  See spec
    for details on conditionally disabling)

 2. Experimental DCC support via dccifd (contributed by Wolfgang Breyha).

 3. There is now a bool{} expansion condition which maps certain strings to
    true/false condition values (most likely of use in conjunction with the
    and{} expansion operator).

 4. The $spam_score, $spam_bar and $spam_report variables are now available
    at delivery time.

 5. exim -bP now supports "macros", "macro_list" or "macro MACRO_NAME" as
    options, provided that Exim is invoked by an admin_user.

 6. There is a new option gnutls_compat_mode, when linked against GnuTLS,
    which increases compatibility with older clients at the cost of decreased
    security.  Don't set this unless you need to support such clients.

 7. There is a new expansion operator, ${randint:...} which will produce a
    "random" number less than the supplied integer.  This randomness is
    not guaranteed to be cryptographically strong, but depending upon how
    Exim was built may be better than the most naive schemes.

 8. Exim now explicitly ensures that SHA256 is available when linked against
    OpenSSL.

 9. The transport_filter_timeout option now applies to SMTP transports too.


Version 4.69
------------

 1. Preliminary DKIM support in Experimental.


Version 4.68
------------

 1. The body_linecount and body_zerocount C variables are now exported in the
    local_scan API.

 2. When a dnslists lookup succeeds, the key that was looked up is now placed
    in $dnslist_matched. When the key is an IP address, it is not reversed in
    this variable (though it is, of course, in the actual lookup). In simple
    cases, for example:

      deny dnslists = spamhaus.example

    the key is also available in another variable (in this case,
    $sender_host_address). In more complicated cases, however, this is not
    true. For example, using a data lookup might generate a dnslists lookup
    like this:

      deny dnslists = spamhaus.example/<|192.168.1.2|192.168.6.7|...

    If this condition succeeds, the value in $dnslist_matched might be
    192.168.6.7 (for example).

 3. Authenticators now have a client_condition option. When Exim is running as
    a client, it skips an authenticator whose client_condition expansion yields
    "0", "no", or "false". This can be used, for example, to skip plain text
    authenticators when the connection is not encrypted by a setting such as:

      client_condition = ${if !eq{$tls_cipher}{}}

    Note that the 4.67 documentation states that $tls_cipher contains the
    cipher used for incoming messages. In fact, during SMTP delivery, it
    contains the cipher used for the delivery. The same is true for
    $tls_peerdn.

 4. There is now a -Mvc <message-id> option, which outputs a copy of the
    message to the standard output, in RFC 2822 format. The option can be used
    only by an admin user.

 5. There is now a /noupdate option for the ratelimit ACL condition. It
    computes the rate and checks the limit as normal, but it does not update
    the saved data. This means that, in relevant ACLs, it is possible to lookup
    the existence of a specified (or auto-generated) ratelimit key without
    incrementing the ratelimit counter for that key.

    In order for this to be useful, another ACL entry must set the rate
    for the same key somewhere (otherwise it will always be zero).

    Example:

    acl_check_connect:
      # Read the rate; if it doesn't exist or is below the maximum
      # we update it below
      deny ratelimit = 100 / 5m / strict / noupdate
           log_message = RATE: $sender_rate / $sender_rate_period \
                         (max $sender_rate_limit)

      [... some other logic and tests...]

      warn ratelimit = 100 / 5m / strict / per_cmd
           log_message = RATE UPDATE: $sender_rate / $sender_rate_period \
                         (max $sender_rate_limit)
           condition = ${if le{$sender_rate}{$sender_rate_limit}}

      accept

 6. The variable $max_received_linelength contains the number of bytes in the
    longest line that was received as part of the message, not counting the
    line termination character(s).

 7. Host lists can now include +ignore_defer and +include_defer, analogous to
    +ignore_unknown and +include_unknown. These options should be used with
    care, probably only in non-critical host lists such as whitelists.

 8. There's a new option called queue_only_load_latch, which defaults true.
    If set false when queue_only_load is greater than zero, Exim re-evaluates
    the load for each incoming message in an SMTP session. Otherwise, once one
    message is queued, the remainder are also.

 9. There is a new ACL, specified by acl_smtp_notquit, which is run in most
    cases when an SMTP session ends without sending QUIT. However, when Exim
    itself is is bad trouble, such as being unable to write to its log files,
    this ACL is not run, because it might try to do things (such as write to
    log files) that make the situation even worse.

    Like the QUIT ACL, this new ACL is provided to make it possible to gather
    statistics. Whatever it returns (accept or deny) is immaterial. The "delay"
    modifier is forbidden in this ACL.

    When the NOTQUIT ACL is running, the variable $smtp_notquit_reason is set
    to a string that indicates the reason for the termination of the SMTP
    connection. The possible values are:

      acl-drop                 Another ACL issued a "drop" command
      bad-commands             Too many unknown or non-mail commands
      command-timeout          Timeout while reading SMTP commands
      connection-lost          The SMTP connection has been lost
      data-timeout             Timeout while reading message data
      local-scan-error         The local_scan() function crashed
      local-scan-timeout       The local_scan() function timed out
      signal-exit              SIGTERM or SIGINT
      synchronization-error    SMTP synchronization error
      tls-failed               TLS failed to start

    In most cases when an SMTP connection is closed without having received
    QUIT, Exim sends an SMTP response message before actually closing the
    connection. With the exception of acl-drop, the default message can be
    overridden by the "message" modifier in the NOTQUIT ACL. In the case of a
    "drop" verb in another ACL, it is the message from the other ACL that is
    used.

10. For MySQL and PostgreSQL lookups, it is now possible to specify a list of
    servers with individual queries. This is done by starting the query with
    "servers=x:y:z;", where each item in the list may take one of two forms:

    (1) If it is just a host name, the appropriate global option (mysql_servers
        or pgsql_servers) is searched for a host of the same name, and the
        remaining parameters (database, user, password) are taken from there.

    (2) If it contains any slashes, it is taken as a complete parameter set.

    The list of servers is used in exactly the same was as the global list.
    Once a connection to a server has happened and a query has been
    successfully executed, processing of the lookup ceases.

    This feature is intended for use in master/slave situations where updates
    are occurring, and one wants to update a master rather than a slave. If the
    masters are in the list for reading, you might have:

      mysql_servers = slave1/db/name/pw:slave2/db/name/pw:master/db/name/pw

    In an updating lookup, you could then write

      ${lookup mysql{servers=master; UPDATE ...}

    If, on the other hand, the master is not to be used for reading lookups:

      pgsql_servers = slave1/db/name/pw:slave2/db/name/pw

    you can still update the master by

      ${lookup pgsql{servers=master/db/name/pw; UPDATE ...}

11. The message_body_newlines option (default FALSE, for backwards
    compatibility) can be used to control whether newlines are present in
    $message_body and $message_body_end. If it is FALSE, they are replaced by
    spaces.


Version 4.67
------------

 1. There is a new log selector called smtp_no_mail, which is not included in
    the default setting. When it is set, a line is written to the main log
    whenever an accepted SMTP connection terminates without having issued a
    MAIL command.

 2. When an item in a dnslists list is followed by = and & and a list of IP
    addresses, the behaviour was not clear when the lookup returned more than
    one IP address. This has been solved by the addition of == and =& for "all"
    rather than the default "any" matching.

 3. Up till now, the only control over which cipher suites GnuTLS uses has been
    for the cipher algorithms. New options have been added to allow some of the
    other parameters to be varied.

 4. There is a new compile-time option called ENABLE_DISABLE_FSYNC. When it is
    set, Exim compiles a runtime option called disable_fsync.

 5. There is a new variable called $smtp_count_at_connection_start.

 6. There's a new control called no_pipelining.

 7. There are two new variables called $sending_ip_address and $sending_port.
    These are set whenever an SMTP connection to another host has been set up.

 8. The expansion of the helo_data option in the smtp transport now happens
    after the connection to the server has been made.

 9. There is a new expansion operator ${rfc2047d: that decodes strings that
    are encoded as per RFC 2047.

10. There is a new log selector called "pid", which causes the current process
    id to be added to every log line, in square brackets, immediately after the
    time and date.

11. Exim has been modified so that it flushes SMTP output before implementing
    a delay in an ACL. It also flushes the output before performing a callout,
    as this can take a substantial time. These behaviours can be disabled by
    obeying control = no_delay_flush or control = no_callout_flush,
    respectively, at some earlier stage of the connection.

12. There are two new expansion conditions that iterate over a list. They are
    called forany and forall.

13. There's a new global option called dsn_from that can be used to vary the
    contents of From: lines in bounces and other automatically generated
    messages ("delivery status notifications" - hence the name of the option).

14. The smtp transport has a new option called hosts_avoid_pipelining.

15. By default, exigrep does case-insensitive matches. There is now a -I option
    that makes it case-sensitive.

16. A number of new features ("addresses", "map", "filter", and "reduce") have
    been added to string expansions to make it easier to process lists of
    items, typically addresses.

17. There's a new ACL modifier called "continue". It does nothing of itself,
    and processing of the ACL always continues with the next condition or
    modifier. It is provided so that the side effects of expanding its argument
    can be used.

18. It is now possible to use newline and other control characters (those with
    values less than 32, plus DEL) as separators in lists.

19. The exigrep utility now has a -v option, which inverts the matching
    condition.

20. The host_find_failed option in the manualroute router can now be set to
    "ignore".


Version 4.66
------------

No new features were added to 4.66.


Version 4.65
------------

No new features were added to 4.65.


Version 4.64
------------

 1. ACL variables can now be given arbitrary names, as long as they start with
    "acl_c" or "acl_m" (for connection variables and message variables), are at
    least six characters long, with the sixth character being either a digit or
    an underscore.

 2. There is a new ACL modifier called log_reject_target. It makes it possible
    to specify which logs are used for messages about ACL rejections.

 3. There is a new authenticator called "dovecot". This is an interface to the
    authentication facility of the Dovecot POP/IMAP server, which can support a
    number of authentication methods.

 4. The variable $message_headers_raw provides a concatenation of all the
    messages's headers without any decoding. This is in contrast to
    $message_headers, which does RFC2047 decoding on the header contents.

 5. In a DNS black list, if two domain names, comma-separated, are given, the
    second is used first to do an initial check, making use of any IP value
    restrictions that are set. If there is a match, the first domain is used,
    without any IP value restrictions, to get the TXT record.

 6. All authenticators now have a server_condition option.

 7. There is a new command-line option called -Mset. It is useful only in
    conjunction with -be (that is, when testing string expansions). It must be
    followed by a message id; Exim loads the given message from its spool
    before doing the expansions.

 8. Another similar new command-line option is called -bem. It operates like
    -be except that it must be followed by the name of a file that contains a
    message.

 9. When an address is delayed because of a 4xx response to a RCPT command, it
    is now the combination of sender and recipient that is delayed in
    subsequent queue runs until its retry time is reached.

10. Unary negation and the bitwise logical operators and, or, xor, not, and
    shift, have been added to the eval: and eval10: expansion items.

11. The variables $interface_address and $interface_port have been renamed
    as $received_ip_address and $received_port, to make it clear that they
    relate to message reception rather than delivery. (The old names remain
    available for compatibility.)

12. The "message" modifier can now be used on "accept" and "discard" acl verbs
    to vary the message that is sent when an SMTP command is accepted.


Version 4.63
------------

1. There is a new Boolean option called filter_prepend_home for the redirect
   router.

2. There is a new acl, set by acl_not_smtp_start, which is run right at the
   start of receiving a non-SMTP message, before any of the message has been
   read.

3. When an SMTP error message is specified in a "message" modifier in an ACL,
   or in a :fail: or :defer: message in a redirect router, Exim now checks the
   start of the message for an SMTP error code.

4. There is a new parameter for LDAP lookups called "referrals", which takes
   one of the settings "follow" (the default) or "nofollow".

5. Version 20070721.2 of exipick now included, offering these new options:
    --reverse
        After all other sorting options have bee processed, reverse order
        before displaying messages (-R is synonym).
    --random
        Randomize order of matching messages before displaying.
    --size
        Instead of displaying the matching messages, display the sum
        of their sizes.
    --sort <variable>[,<variable>...]
        Before displaying matching messages, sort the messages according to
        each messages value for each variable.
    --not
        Negate the value for every test (returns inverse output from the
        same criteria without --not).


Version 4.62
------------

1. The ${readsocket expansion item now supports Internet domain sockets as well
   as Unix domain sockets. If the first argument begins "inet:", it must be of
   the form "inet:host:port". The port is mandatory; it may be a number or the
   name of a TCP port in /etc/services. The host may be a name, or it may be an
   IP address. An ip address may optionally be enclosed in square brackets.
   This is best for IPv6 addresses. For example:

     ${readsocket{inet:[::1]:1234}{<request data>}...

   Only a single host name may be given, but if looking it up yield more than
   one IP address, they are each tried in turn until a connection is made. Once
   a connection has been made, the behaviour is as for ${readsocket with a Unix
   domain socket.

2. If a redirect router sets up file or pipe deliveries for more than one
   incoming address, and the relevant transport has batch_max set greater than
   one, a batch delivery now occurs.

3. The appendfile transport has a new option called maildirfolder_create_regex.
   Its value is a regular expression. For a maildir delivery, this is matched
   against the maildir directory; if it matches, Exim ensures that a
   maildirfolder file is created alongside the new, cur, and tmp directories.


Version 4.61
------------

The documentation is up-to-date for the 4.61 release. Major new features since
the 4.60 release are:

. An option called disable_ipv6, to disable the use of IPv6 completely.

. An increase in the number of ACL variables to 20 of each type.

. A change to use $auth1, $auth2, and $auth3 in authenticators instead of $1,
  $2, $3, (though those are still set) because the numeric variables get used
  for other things in complicated expansions.

. The default for rfc1413_query_timeout has been changed from 30s to 5s.

. It is possible to use setclassresources() on some BSD OS to control the
  resources used in pipe deliveries.

. A new ACL modifier called add_header, which can be used with any verb.

. More errors are detectable in retry rules.

There are a number of other additions too.


Version 4.60
------------

The documentation is up-to-date for the 4.60 release. Major new features since
the 4.50 release are:

. Support for SQLite.

. Support for IGNOREQUOTA in LMTP.

. Extensions to the "submission mode" features.

. Support for Client SMTP Authorization (CSA).

. Support for ratelimiting hosts and users.

. New expansion items to help with the BATV "prvs" scheme.

. A "match_ip" condition, that matches an IP address against a list.

There are many more minor changes.

****