X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/cf00dad6749f2b3c2ba9b1e02034b23944b7ee0c..8800895ae8a1e9c49c739839a6623292d7a473d0:/doc/doc-txt/NewStuff

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--- a/doc/doc-txt/NewStuff
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@@ -1,4 +1,4 @@
-$Cambridge: exim/doc/doc-txt/NewStuff,v 1.33 2005/04/05 13:58:34 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/NewStuff,v 1.67 2005/09/12 10:08:53 ph10 Exp $
 
 New Features in Exim
 --------------------
@@ -8,6 +8,537 @@ but have not yet made it into the main manual (which is most conveniently
 updated when there is a relatively large batch of changes). The doc/ChangeLog
 file contains a listing of all changes, including bug fixes.
 
+Exim version 4.53
+-----------------
+
+TK/01 Added the "success_on_redirect" address verification option. When an
+      address generates new addresses during routing, Exim will abort
+      verification with "success" when more than one address has been
+      generated, but continue to verify a single new address. The latter
+      does not happen when the new "success_on_redirect" option is set, like
+
+      require verify = recipient/success_on_redirect/callout=10s
+
+      In that case, verification will succeed when a router generates a new
+      address.
+
+PH/01 Support for SQLite database lookups has been added. This is another
+      query-style lookup, but it is slightly different from the others because
+      a file name is required in addition to the SQL query. This is because an
+      SQLite database is a single file and there is no daemon as in other SQL
+      databases. The interface to Exim requires the name of the file, as an
+      absolute path, to be given at the start of the query. It is separated
+      from the query by white space. This means that the path name cannot
+      contain white space. Here is a lookup expansion example:
+
+        ${lookup sqlite {/some/thing/sqlitedb \
+          select name from aliases where id='ph10';}}
+
+      In a list, the syntax is similar. For example:
+
+        domainlist relay_domains = sqlite;/some/thing/sqlitedb \
+           select * from relays where ip='$sender_host_address';
+
+      The only character affected by the ${quote_sqlite: operator is a single
+      quote, which it doubles.
+
+      The SQLite library handles multiple simultaneous accesses to the database
+      internally. Multiple readers are permitted, but only one process can
+      update at once. Attempts to access the database while it is being updated
+      are rejected after a timeout period, during which the SQLite library
+      waits for the lock to be released. In Exim, the default timeout is set
+      to 5 seconds, but it can be changed by means of the sqlite_lock_timeout
+      option.
+
+      Note that you must set LOOKUP_SQLITE=yes in Local/Makefile in order to
+      obtain SQLite support, and you will also need to add -lsqlite3 to the
+      EXTRALIBS setting. And of course, you have to install SQLite on your
+      host first.
+
+PH/02 The variable $message_id is now deprecated, to be replaced by
+      $message_exim_id, which makes it clearer which ID is being referenced.
+
+PH/03 The use of forbid_filter_existstest now also locks out the use of the
+      ${stat: expansion item.
+
+PH/04 The IGNOREQUOTA extension to the LMTP protocol is now available in both
+      the lmtp transport and the smtp transport running in LMTP mode. In the
+      lmtp transport there is a new Boolean option called ignore_quota, and in
+      the smtp transport there is a new Boolean option called
+      lmtp_ignore_quota. If either of these options is set TRUE, the string
+      "IGNOREQUOTA" is added to RCPT commands when using the LMTP protocol,
+      provided that the server has advertised support for IGNOREQUOTA in its
+      response to the LHLO command.
+
+PH/05 Previously, if "verify = helo" was set in an ACL, the condition was true
+      only if the host matched helo_try_verify_hosts, which caused the
+      verification to occur when the EHLO/HELO command was issued. The ACL just
+      tested the remembered result. Now, if a previous verification attempt has
+      not happened, "verify = helo" does it there and then.
+
+PH/06 It is now possible to specify a port number along with a host name or
+      IP address in the list of hosts defined in the manualroute or
+      queryprogram routers, fallback_hosts, or the "hosts" option of the smtp
+      transport. These all override any port specification on the transport.
+      The relatively standard syntax of using a colon separator has been
+      adopted, but there are some gotchas that need attention:
+
+      * In all these lists of hosts, colon is the default separator, so either
+        the colon that specifies a port must be doubled, or the separator must
+        be changed. The following two examples have the same effect:
+
+          fallback_hosts = host1.tld::1225 : host2.tld::1226
+          fallback_hosts = <; host1.tld:1225 ; host2.tld:1226
+
+      * When IPv6 addresses are involved, it gets worse, because they contain
+        colons of their own. To make this case easier, it is permitted to
+        enclose an IP address (either v4 or v6) in square brackets if a port
+        number follows. Here's an example from a manualroute router:
+
+           route_list = * "</ [10.1.1.1]:1225 / [::1]:1226"
+
+      If the "/MX" feature is to be used as well as a port specifier, the port
+      must come last. For example:
+
+           route_list = *  dom1.tld/mx::1225
+
+PH/07 $smtp_command_argument is now set for all SMTP commands, not just the
+      non-message ones. This makes it possible to inspect the complete command
+      for RCPT commands, for example.
+
+PH/08 The ${eval expansion now supports % as a "remainder" operator.
+
+PH/09 There is a new ACL condition "verify = not_blind". It checks that there
+      are no blind (bcc) recipients in the message. Every envelope recipient
+      must appear either in a To: header line or in a Cc: header line for this
+      condition to be true. Local parts are checked case-sensitively; domains
+      are checked case-insensitively. If Resent-To: or Resent-Cc: header lines
+      exist, they are also checked. This condition can be used only in a DATA
+      or non-SMTP ACL.
+
+      There are, of course, many legitimate messages that make use of blind
+      (bcc) recipients. This check should not be used on its own for blocking
+      messages.
+
+PH/10 There is a new ACL control called "suppress_local_fixups". This applies
+      to locally submitted (non TCP/IP) messages, and is the complement of
+      "control = submission". It disables the fixups that are normally applied
+      to locally-submitted messages. Specifically:
+
+      (a) Any Sender: header line is left alone (in this respect, it's a
+          dynamic version of local_sender_retain).
+
+      (b) No Message-ID:, From:, or Date: headers are added.
+
+      (c) There is no check that From: corresponds to the actual sender.
+
+      This feature may be useful when a remotely-originated message is
+      accepted, passed to some scanning program, and then re-submitted for
+      delivery. It means that all four possibilities can now be specified:
+
+      (1) Locally submitted, fixups applies: the default.
+      (2) Locally submitted, no fixups applied: use control =
+          suppress_local_fixups.
+      (3) Remotely submitted, no fixups applied: the default.
+      (4) Remotely submitted, fixups applied: use control = submission.
+
+
+Exim version 4.52
+-----------------
+
+TF/01 Support for checking Client SMTP Authorization has been added. CSA is a
+      system which allows a site to advertise which machines are and are not
+      permitted to send email. This is done by placing special SRV records in
+      the DNS, which are looked up using the client's HELO domain. At this
+      time CSA is still an Internet-Draft.
+
+      Client SMTP Authorization checks are performed by the ACL condition
+      verify=csa. This will fail if the client is not authorized. If there is
+      a DNS problem, or if no valid CSA SRV record is found, or if the client
+      is authorized, the condition succeeds. These three cases can be
+      distinguished using the expansion variable $csa_status, which can take
+      one of the values "fail", "defer", "unknown", or "ok". The condition
+      does not itself defer because that would be likely to cause problems
+      for legitimate email.
+
+      The error messages produced by the CSA code include slightly more
+      detail. If $csa_status is "defer" this may be because of problems
+      looking up the CSA SRV record, or problems looking up the CSA target
+      address record. There are four reasons for $csa_status being "fail":
+      the client's host name is explicitly not authorized; the client's IP
+      address does not match any of the CSA target IP addresses; the client's
+      host name is authorized but it has no valid target IP addresses (e.g.
+      the target's addresses are IPv6 and the client is using IPv4); or the
+      client's host name has no CSA SRV record but a parent domain has
+      asserted that all subdomains must be explicitly authorized.
+
+      The verify=csa condition can take an argument which is the domain to
+      use for the DNS query. The default is verify=csa/$sender_helo_name.
+
+      This implementation includes an extension to CSA. If the query domain
+      is an address literal such as [192.0.2.95], or if it is a bare IP
+      address, Exim will search for CSA SRV records in the reverse DNS as if
+      the HELO domain was e.g. 95.2.0.192.in-addr.arpa. Therefore it is
+      meaningful to say, for example, verify=csa/$sender_host_address - in
+      fact, this is the check that Exim performs if the client does not say
+      HELO. This extension can be turned off by setting the main
+      configuration option dns_csa_use_reverse = false.
+
+      If a CSA SRV record is not found for the domain itself, then a search
+      is performed through its parent domains for a record which might be
+      making assertions about subdomains. The maximum depth of this search is
+      limited using the main configuration option dns_csa_search_limit, which
+      takes the value 5 by default. Exim does not look for CSA SRV records in
+      a top level domain, so the default settings handle HELO domains as long
+      as seven (hostname.five.four.three.two.one.com) which encompasses the
+      vast majority of legitimate HELO domains.
+
+      The dnsdb lookup also has support for CSA. Although dnsdb already
+      supports SRV lookups, this is not sufficient because of the extra
+      parent domain search behaviour of CSA, and (as with PTR lookups)
+      dnsdb also turns IP addresses into lookups in the reverse DNS space.
+      The result of ${lookup dnsdb {csa=$sender_helo_name} } has two
+      space-separated fields: an authorization code and a target host name.
+      The authorization code can be "Y" for yes, "N" for no, "X" for explicit
+      authorization required but absent, or "?" for unknown.
+
+PH/01 The amount of output produced by the "make" process has been reduced,
+      because the compile lines are often rather long, making it all pretty
+      unreadable. The new style is along the lines of the 2.6 Linux kernel:
+      just a short line for each module that is being compiled or linked.
+      However, it is still possible to get the full output, by calling "make"
+      like this:
+
+        FULLECHO='' make -e
+
+      The value of FULLECHO defaults to "@", the flag character that suppresses
+      command reflection in "make". When you ask for the full output, it is
+      given in addition to the the short output.
+
+TF/02 There have been two changes concerned with submission mode:
+
+      Until now submission mode always left the return path alone, whereas
+      locally-submitted messages from untrusted users have the return path
+      fixed to the user's email address. Submission mode now fixes the return
+      path to the same address as is used to create the Sender: header. If
+      /sender_retain is specified then both the Sender: header and the return
+      path are left alone.
+
+      Note that the changes caused by submission mode take effect after the
+      predata ACL. This means that any sender checks performed before the
+      fix-ups will use the untrusted sender address specified by the user, not
+      the trusted sender address specified by submission mode. Although this
+      might be slightly unexpected, it does mean that you can configure ACL
+      checks to spot that a user is trying to spoof another's address, for
+      example.
+
+      There is also a new /name= option for submission mode which allows you
+      to specify the user's full name to be included in the Sender: header.
+      For example:
+
+        accept authenticated = *
+               control = submission/name=${lookup {$authenticated_id} \
+                                           lsearch {/etc/exim/namelist} }
+
+      The namelist file contains entries like
+
+        fanf: Tony Finch
+
+      And the resulting Sender: header looks like
+
+        Sender: Tony Finch <fanf@exim.org>
+
+TF/03 The control = fakereject ACL modifier now has a fakedefer counterpart,
+      which works in exactly the same way except it causes a fake SMTP 450
+      response after the message data instead of a fake SMTP 550 response.
+      You must take care when using fakedefer because it will cause messages
+      to be duplicated when the sender retries. Therefore you should not use
+      fakedefer if the message will be delivered normally.
+
+TF/04 There is a new ratelimit ACL condition which can be used to measure
+      and control the rate at which clients can send email. This is more
+      powerful than the existing smtp_ratelimit_* options, because those
+      options only control the rate of commands in a single SMTP session,
+      whereas the new ratelimit condition works across all connections
+      (concurrent and sequential) to the same host.
+
+      The syntax of the ratelimit condition is:
+
+        ratelimit = <m> / <p> / <options> / <key>
+
+      If the average client sending rate is less than m messages per time
+      period p then the condition is false, otherwise it is true.
+
+      The parameter p is the smoothing time constant, in the form of an Exim
+      time interval e.g. 8h for eight hours. A larger time constant means it
+      takes Exim longer to forget a client's past behaviour. The parameter m is
+      the maximum number of messages that a client can send in a fast burst. By
+      increasing both m and p but keeping m/p constant, you can allow a client
+      to send more messages in a burst without changing its overall sending
+      rate limit. Conversely, if m and p are both small then messages must be
+      sent at an even rate.
+
+      The key is used to look up the data used to calcluate the client's
+      average sending rate. This data is stored in a database maintained by
+      Exim in its spool directory alongside the retry database etc. For
+      example, you can limit the sending rate of each authenticated user,
+      independent of the computer they are sending from, by setting the key
+      to $authenticated_id. The default key is $sender_host_address.
+      Internally, Exim includes the smoothing constant p and the options in
+      the lookup key because they alter the meaning of the stored data.
+      This is not true for the limit m, so you can alter the configured
+      maximum rate and Exim will still remember clients' past behaviour,
+      but if you alter the other ratelimit parameters Exim will effectively
+      forget their past behaviour.
+
+      Each ratelimit condition can have up to two options. The first option
+      specifies what Exim measures the rate of, and the second specifies how
+      Exim handles excessively fast clients.
+
+      The per_mail option means that it measures the client's rate of sending
+      messages. This is the default if none of the per_* options is specified.
+
+      The per_conn option means that it measures the client's connection rate.
+
+      The per_byte option limits the sender's email bandwidth. Note that it
+      is best to use this option in the DATA ACL; if it is used in an earlier
+      ACL it relies on the SIZE parameter on the MAIL command, which may be
+      inaccurate or completely missing. You can follow the limit m in the
+      configuration with K, M, or G to specify limits in kilobytes,
+      megabytes, or gigabytes respectively.
+
+      The per_cmd option means that Exim recomputes the rate every time the
+      condition is processed, which can be used to limit the SMTP command rate.
+      The alias per_rcpt is provided for use in the RCPT ACL instead of per_cmd
+      to make it clear that the effect is to limit the rate at which recipients
+      are accepted. Note that in this case the rate limiting engine will see a
+      message with many recipients as a large high-speed burst.
+
+      If a client's average rate is greater than the maximum, the rate
+      limiting engine can react in two possible ways, depending on the
+      presence of the strict or leaky options. This is independent of the
+      other counter-measures (e.g. rejecting the message) that may be
+      specified by the rest of the ACL. The default mode is leaky, which
+      avoids a sender's over-aggressive retry rate preventing it from getting
+      any email through.
+
+      The strict option means that the client's recorded rate is always
+      updated. The effect of this is that Exim measures the client's average
+      rate of attempts to send email, which can be much higher than the
+      maximum. If the client is over the limit it will be subjected to
+      counter-measures until it slows down below the maximum rate.
+
+      The leaky option means that the client's recorded rate is not updated
+      if it is above the limit. The effect of this is that Exim measures the
+      client's average rate of successfully sent email, which cannot be
+      greater than the maximum. If the client is over the limit it will
+      suffer some counter-measures, but it will still be able to send email
+      at the configured maximum rate, whatever the rate of its attempts.
+
+      As a side-effect, the ratelimit condition will set the expansion
+      variables $sender_rate containing the client's computed rate,
+      $sender_rate_limit containing the configured value of m, and
+      $sender_rate_period containing the configured value of p.
+
+      Exim's other ACL facilities are used to define what counter-measures
+      are taken when the rate limit is exceeded. This might be anything from
+      logging a warning (e.g. while measuring existing sending rates in order
+      to define our policy), through time delays to slow down fast senders,
+      up to rejecting the message. For example,
+
+        # Log all senders' rates
+        warn
+          ratelimit = 0 / 1h / strict
+          log_message = \
+            Sender rate $sender_rate > $sender_rate_limit / $sender_rate_period
+
+        # Slow down fast senders
+        warn
+          ratelimit = 100 / 1h / per_rcpt / strict
+          delay     = ${eval: 10 * ($sender_rate - $sender_rate_limit) }
+
+        # Keep authenticated users under control
+        deny
+          ratelimit = 100 / 1d / strict / $authenticated_id
+
+        # System-wide rate limit
+        defer
+          message = Sorry, too busy. Try again later.
+          ratelimit = 10 / 1s / $primary_hostname
+
+        # Restrict incoming rate from each host, with a default rate limit
+        # set using a macro and special cases looked up in a table.
+        defer
+          message = Sender rate $sender_rate exceeds \
+                    $sender_rate_limit messages per $sender_rate_period
+          ratelimit = ${lookup {$sender_host_address} \
+                        cdb {DB/ratelimits.cdb} \
+                        {$value} {RATELIMIT} }
+
+      Warning: if you have a busy server with a lot of ratelimit tests,
+      especially with the per_rcpt option, you may suffer from a performance
+      bottleneck caused by locking on the ratelimit hints database. Apart from
+      making your ACLs less complicated, you can reduce the problem by using a
+      RAM disk for Exim's hints directory, /var/spool/exim/db/. However this
+      means that Exim will lose its hints data after a reboot (including retry
+      hints, the callout cache, and ratelimit data).
+
+TK/01 Added an 'spf' lookup type that will return an SPF result for a given
+      email address (the key) and an IP address (the database):
+
+      ${lookup {tom@duncanthrax.net} spf{217.115.139.137}}
+
+      The lookup will return the same result strings as they can appear in
+      $spf_result (pass,fail,softfail,neutral,none,err_perm,err_temp). The
+      lookup is armored in EXPERIMENTAL_SPF. Currently, only IPv4 addresses
+      are supported.
+
+      Patch submitted by Chris Webb <chris@arachsys.com>.
+
+PH/02 There's a new verify callout option, "fullpostmaster", which first acts
+      as "postmaster" and checks the recipient <postmaster@domain>. If that
+      fails, it tries just <postmaster>, without a domain, in accordance with
+      the specification in RFC 2821.
+
+PH/03 The action of the auto_thaw option has been changed. It no longer applies
+      to frozen bounce messages.
+
+TK/02 There are two new expansion items to help with the implementation of
+      the BATV "prvs" scheme in an Exim configuration:
+
+
+      ${prvs {<ADDRESS>}{<KEY>}{[KEYNUM]}}
+
+      The "prvs" expansion item takes three arguments: A qualified RFC2821
+      email address, a key and an (optional) key number. All arguments are
+      expanded before being used, so it is easily possible to lookup a key
+      and key number using the address as the lookup key. The key number is
+      optional and defaults to "0". The item will expand to a "prvs"-signed
+      email address, to be typically used with the "return_path" option on
+      a smtp transport. The decision if BATV should be used with a given
+      sender/recipient pair should be done on router level, to avoid having
+      to set "max_rcpt = 1" on the transport.
+
+
+      ${prvscheck {<ADDRESS>}{<SECRET>}{<RETURN_STRING>}}
+
+      The "prvscheck" expansion item takes three arguments. Argument 1 is
+      expanded first. When the expansion does not yield a SYNTACTICALLY
+      valid "prvs"-scheme address, the whole "prvscheck" item expands to
+      the empty string. If <ADDRESS> is a "prvs"-encoded address after
+      expansion, two expansion variables are set up:
+
+        $prvscheck_address   Contains the "prvs"-decoded version of
+                             the address from argument 1.
+
+        $prvscheck_keynum    Contains the key number extracted from
+                             the "prvs"-address in argument 1.
+
+      These two variables can be used in the expansion code of argument 2
+      to retrieve the <SECRET>. The VALIDITY of the "prvs"-signed address
+      is then checked. The result is stored in yet another expansion
+      variable:
+
+        $prvscheck_result    Contains the result of a "prvscheck"
+                             expansion: Unset (the empty string) for
+                             failure, "1" for success.
+
+      The "prvscheck" expansion expands to the empty string if <ADDRESS>
+      is not a SYNTACTICALLY valid "prvs"-scheme address. Otherwise,
+      argument 3 defines what "prvscheck" expands to: If argument 3
+      is the empty string, "prvscheck" expands to the decoded version
+      of the address (no matter if it is CRYPTOGRAPHICALLY valid or not).
+      If argument 3 expands to a non-empty string, "prvscheck" expands
+      to that string.
+
+
+      Usage example
+      -------------
+
+      Macro:
+
+      PRVSCHECK_SQL = ${lookup mysql{SELECT secret FROM batv_prvs WHERE \
+                      sender='${quote_mysql:$prvscheck_address}'}{$value}}
+
+      RCPT ACL:
+
+      # Bounces: drop unsigned addresses for BATV senders
+      deny message = This address does not send an unsigned reverse path.
+           senders = :
+           recipients = +batv_recipients
+
+      # Bounces: In case of prvs-signed address, check signature.
+      deny message = Invalid reverse path signature.
+           senders = :
+           condition = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{1}}
+           !condition = $prvscheck_result
+
+      Top-Level Router:
+
+      batv_redirect:
+        driver = redirect
+        data = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{}}
+
+      Transport (referenced by router that makes decision if
+      BATV is applicable):
+
+        external_smtp_batv:
+          driver = smtp
+          return_path = ${prvs {$return_path} \
+                               {${lookup mysql{SELECT \
+                               secret FROM batv_prvs WHERE \
+                               sender='${quote_mysql:$sender_address}'} \
+                           {$value}fail}}}
+
+PH/04 There are two new options that control the retrying done by the daemon
+      at startup when it cannot immediately bind a socket (typically because
+      the socket is already in use). The default values reproduce what were
+      built-in constants previously: daemon_startup_retries defines the number
+      of retries after the first failure (default 9); daemon_startup_sleep
+      defines the length of time to wait between retries (default 30s).
+
+PH/05 There is now a new ${if condition called "match_ip". It is similar to
+      match_domain, etc. It must be followed by two argument strings. The first
+      (after expansion) must be an IP address or an empty string. The second
+      (after expansion) is a restricted host list that can match only an IP
+      address, not a host name. For example:
+
+        ${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}}
+
+      The specific types of host list item that are permitted in the list are
+      shown below. Consult the manual section on host lists for further
+      details.
+
+      . An IP address, optionally with a CIDR mask.
+
+      . A single asterisk matches any IP address.
+
+      . An empty item matches only if the IP address is empty. This could be
+        useful for testing for a locally submitted message or one from specific
+        hosts in a single test such as
+
+          ${if match_ip{$sender_host_address}{:4.3.2.1:...}{...}{...}}
+
+        where the first item in the list is the empty string.
+
+      . The item @[] matches any of the local host's interface addresses.
+
+      . Lookups are assumed to be "net-" style lookups, even if "net-" is not
+        specified. Thus, the following are equivalent:
+
+          ${if match_ip{$sender_host_address}{lsearch;/some/file}...
+          ${if match_ip{$sender_host_address}{net-lsearch;/some/file}...
+
+        You do need to specify the "net-" prefix if you want to specify a
+        specific address mask, for example, by using "net24-".
+
+PH/06 The "+all" debug selector used to set the flags for all possible output;
+      it is something that people tend to use semi-automatically when
+      generating debug output for me or for the list. However, by including
+      "+memory", an awful lot of output that is very rarely of interest was
+      generated. I have changed this so that "+all" no longer includes
+      "+memory". However, "-all" still turns everything off.
+
 
 Version 4.51
 ------------
@@ -130,6 +661,57 @@ PH/06 Macros may now be defined or redefined between router, transport,
       driver or ACL, or in the local_scan, retry, or rewrite sections of the
       configuration.
 
+PH/07 $acl_verify_message is now set immediately after the failure of a
+      verification in an ACL, and so is available in subsequent modifiers. In
+      particular, the message can be preserved by coding like this:
+
+         warn  !verify = sender
+               set acl_m0 = $acl_verify_message
+
+      Previously, $acl_verify_message was set only while expanding "message"
+      and "log_message" when a very denied access.
+
+PH/08 The redirect router has two new options, sieve_useraddress and
+      sieve_subaddress. These are passed to a Sieve filter to specify the :user
+      and :subaddress parts of an address. Both options are unset by default.
+      However, when a Sieve filter is run, if sieve_useraddress is unset, the
+      entire original local part (including any prefix or suffix) is used for
+      :user. An unset subaddress is treated as an empty subaddress.
+
+PH/09 Quota values can be followed by G as well as K and M.
+
+PH/10 $message_linecount is a new variable that contains the total number of
+      lines in the header and body of the message. Compare $body_linecount,
+      which is the count for the body only. During the DATA and
+      content-scanning ACLs, $message_linecount contains the number of lines
+      received. Before delivery happens (that is, before filters, routers, and
+      transports run) the count is increased to include the Received: header
+      line that Exim standardly adds, and also any other header lines that are
+      added by ACLs. The blank line that separates the message header from the
+      body is not counted. Here is an example of the use of this variable in a
+      DATA ACL:
+
+        deny message   = Too many lines in message header
+             condition = \
+               ${if <{250}{${eval: $message_linecount - $body_linecount}}}
+
+      In the MAIL and RCPT ACLs, the value is zero because at that stage the
+      message has not yet been received.
+
+PH/11 In a ${run expansion, the variable $value (which contains the standard
+      output) is now also usable in the "else" string.
+
+PH/12 In a pipe transport, although a timeout while waiting for the pipe
+      process to complete was treated as a delivery failure, a timeout while
+      writing the message to the pipe was logged, but erroneously treated as a
+      successful delivery. Such timeouts include transport filter timeouts. For
+      consistency with the overall process timeout, these timeouts are now
+      treated as errors, giving rise to delivery failures by default. However,
+      there is now a new Boolean option for the pipe transport called
+      timeout_defer, which, if set TRUE, converts the failures into defers for
+      both kinds of timeout. A transport filter timeout is now identified in
+      the log output.
+
 
 Version 4.50
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