The next two lines are concerned with &'ident'& callbacks, as defined by RFC
1413 (hence their names):
.code
-rfc1413_hosts = *
-rfc1413_query_timeout = 5s
+rfc1413_query_hosts = *
+rfc1413_query_timeout = 0s
+.endd
+These settings cause Exim to avoid ident callbacks for all incoming SMTP calls.
+Few hosts offer RFC1413 service these days; calls have to be
+terminated by a timeout and this needlessly delays the startup
+of an incoming SMTP connection.
+If you have hosts for which you trust RFC1413 and need this
+information, you can change this.
+
+This line enables an efficiency SMTP option. It is negociated by clients
+and not expected to cause problems but can be disabled if needed.
+.code
+prdr_enable = true
.endd
-These settings cause Exim to make ident callbacks for all incoming SMTP calls.
-You can limit the hosts to which these calls are made, or change the timeout
-that is used. If you set the timeout to zero, all ident calls are disabled.
-Although they are cheap and can provide useful information for tracing problem
-messages, some hosts and firewalls have problems with ident calls. This can
-result in a timeout instead of an immediate refused connection, leading to
-delays on starting up an incoming SMTP session.
When Exim receives messages over SMTP connections, it expects all addresses to
be fully qualified with a domain, as required by the SMTP definition. However,
.code
remote_smtp:
driver = smtp
+ hosts_try_prdr = *
.endd
-This transport is used for delivering messages over SMTP connections. All its
-options are defaulted. The list of remote hosts comes from the router.
+This transport is used for delivering messages over SMTP connections.
+The list of remote hosts comes from the router.
+The &%hosts_try_prdr%& option enables an efficiency SMTP option.
+It is negotiated between client and server
+and not expected to cause problems but can be disabled if needed.
+All other options are defaulted.
.code
local_delivery:
driver = appendfile
.display
&`version `&
&`serial_number `&
-&`subject `&
-&`issuer `&
-&`notbefore `&
-&`notafter `&
+&`subject `& RFC4514 DN
+&`issuer `& RFC4514 DN
+&`notbefore `& time
+&`notafter `& time
&`sig_algorithm `&
&`signature `&
&`subj_altname `& tagged list
Some field names take optional modifiers, appended and separated by commas.
+The field selectors marked as "RFC4514" above
+output a Distinguished Name string which is
+not quite
+parseable by Exim as a comma-separated tagged list
+(the exceptions being elements containin commas).
+RDN elements of a single type may be selected by
+a modifier of the type label; if so the expansion
+result is a list (newline-separated by default).
+The separator may be changed by another modifer of
+a right angle-bracket followed immediately by the new separator.
+Recognised RDN type labels include "CN", "O", "OU" and "DC".
+
+The field selectors marked as "time" above
+may output a number of seconds since epoch
+if the modifier "int" is used.
+
The field selectors marked as "list" above return a list,
newline-separated by default,
(embedded separator characters in elements are doubled).
which is one of "dns", "uri" or "mail";
if so the elenment tags are omitted.
-Field values are generally presented in human-readable form.
+If not otherwise noted field values are presented in human-readable form.
.wen
.vitem "&*${dlfunc{*&<&'file'&>&*}{*&<&'function'&>&*}{*&<&'arg'&>&*}&&&
{*&<&'string2'&>&*}}*&"
.cindex "expansion" "running a command"
.cindex "&%run%& expansion item"
-The command and its arguments are first expanded separately, and then the
-command is run in a separate process, but under the same uid and gid. As in
-other command executions from Exim, a shell is not used by default. If you want
+.new
+The command and its arguments are first expanded as one string. The string is
+split apart into individual arguments by spaces, and then the command is run
+in a separate process, but under the same uid and gid. As in other command
+executions from Exim, a shell is not used by default. If the command requires
a shell, you must explicitly code it.
+Since the arguments are split by spaces, when there is a variable expansion
+which has an empty result, it will cause the situation that the argument will
+simply be omitted when the program is actually executed by Exim. If the
+script/program requires a specific number of arguments and the expanded
+variable could possibly result in this empty expansion, the variable must be
+quoted. This is more difficult if the expanded variable itself could result
+in a string containing quotes, because it would interfere with the quotes
+around the command arguments. A possible guard against this is to wrap the
+variable in the &%sg%& operator to change any quote marks to some other
+character.
+.wen
+
The standard input for the command exists, but is empty. The standard output
and standard error are set to the same file descriptor.
.cindex "return code" "from &%run%& expansion"
.vitem &$sender_host_dnssec$&
.vindex "&$sender_host_dnssec$&"
-If &$sender_host_name$& has been populated (by reference, &%hosts_lookup%& or
+If an attempt to populate &$sender_host_name$& has been made
+(by reference, &%hosts_lookup%& or
otherwise) then this boolean will have been set true if, and only if, the
resolver library states that the reverse DNS was authenticated data. At all
other times, this variable is false.
following options:
.ilist
-&%daemon_smtp_ports%& contains a list of default ports. (For backward
-compatibility, this option can also be specified in the singular.)
+&%daemon_smtp_ports%& contains a list of default ports
+or service names.
+(For backward compatibility, this option can also be specified in the singular.)
.next
&%local_interfaces%& contains list of interface IP addresses on which to
listen. Each item may optionally also specify a port.
Exim supports the obsolete SSMTP protocol (also known as SMTPS) that was used
before the STARTTLS command was standardized for SMTP. Some legacy clients
still use this protocol. If the &%tls_on_connect_ports%& option is set to a
-list of port numbers, connections to those ports must use SSMTP. The most
+list of port numbers or service names,
+connections to those ports must use SSMTP. The most
common use of this option is expected to be
.code
tls_on_connect_ports = 465
.row &%tls_crl%& "certificate revocation list"
.row &%tls_dh_max_bits%& "clamp D-H bit count suggestion"
.row &%tls_dhparam%& "DH parameters for server"
+.row &%tls_ocsp_file%& "location of server certificate status proof"
.row &%tls_on_connect_ports%& "specify SSMTP (SMTPS) ports"
.row &%tls_privatekey%& "location of server private key"
.row &%tls_remember_esmtp%& "don't reset after starting TLS"
acceptable bound from 1024 to 2048.
+.option tls_ocsp_file main string&!! unset
+This option
+must if set expand to the absolute path to a file which contains a current
+status proof for the server's certificate, as obtained from the
+Certificate Authority.
+
+
.option tls_on_connect_ports main "string list" unset
This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately
&<<CHAPSMTPAUTH>>& for details of authentication.
+.option hosts_request_ocsp smtp "host list&!!" *
+.cindex "TLS" "requiring for certain servers"
+Exim will request a Certificate Status on a
+TLS session for any host that matches this list.
+&%tls_verify_certificates%& should also be set for the transport.
+
+.option hosts_require_ocsp smtp "host list&!!" unset
+.cindex "TLS" "requiring for certain servers"
+Exim will request, and check for a valid Certificate Status being given, on a
+TLS session for any host that matches this list.
+&%tls_verify_certificates%& should also be set for the transport.
+
.option hosts_require_tls smtp "host list&!!" unset
.cindex "TLS" "requiring for certain servers"
Exim will insist on using a TLS session when delivering to any host that
This option gives a list of hosts for which, on encrypted connections,
certificate verification will be tried but need not succeed.
The &%tls_verify_certificates%& option must also be set.
+Note that unless the host is in this list
+TLS connections will be denied to hosts using self-signed certificates
+when &%tls_verify_certificates%& is set.
+The &$tls_out_certificate_verified$& variable is set when
+certificate verification succeeds.
.option tls_verify_certificates smtp string&!! unset
driver = dovecot
public_name = PLAIN
server_socket = /var/run/dovecot/auth-client
- server_set_id = $auth2
+ server_set_id = $auth1
dovecot_ntlm:
driver = dovecot
.cindex "TLS" "revoked certificates"
.cindex "revocation list"
.cindex "certificate" "revocation list"
+.cindex "OCSP" "stapling"
Certificate issuing authorities issue Certificate Revocation Lists (CRLs) when
certificates are revoked. If you have such a list, you can pass it to an Exim
server using the global option called &%tls_crl%& and to an Exim client using
an identically named option for the &(smtp)& transport. In each case, the value
of the option is expanded and must then be the name of a file that contains a
CRL in PEM format.
+The downside is that clients have to periodically re-download a potentially huge
+file from every certificate authority the know of.
+
+The way with most moving parts at query time is Online Certificate
+Status Protocol (OCSP), where the client verifies the certificate
+against an OCSP server run by the CA. This lets the CA track all
+usage of the certs. It requires running software with access to the
+private key of the CA, to sign the responses to the OCSP queries. OCSP
+is based on HTTP and can be proxied accordingly.
+
+The only widespread OCSP server implementation (known to this writer)
+comes as part of OpenSSL and aborts on an invalid request, such as
+connecting to the port and then disconnecting. This requires
+re-entering the passphrase each time some random client does this.
+
+The third way is OCSP Stapling; in this, the server using a certificate
+issued by the CA periodically requests an OCSP proof of validity from
+the OCSP server, then serves it up inline as part of the TLS
+negotiation. This approach adds no extra round trips, does not let the
+CA track users, scales well with number of certs issued by the CA and is
+resilient to temporary OCSP server failures, as long as the server
+starts retrying to fetch an OCSP proof some time before its current
+proof expires. The downside is that it requires server support.
+
+Unless Exim is built with the support disabled,
+or with GnuTLS earlier than version 3.1.3,
+support for OCSP stapling is included.
+
+There is a global option called &%tls_ocsp_file%&.
+The file specified therein is expected to be in DER format, and contain
+an OCSP proof. Exim will serve it as part of the TLS handshake. This
+option will be re-expanded for SNI, if the &%tls_certificate%& option
+contains &`tls_in_sni`&, as per other TLS options.
+
+Exim does not at this time implement any support for fetching a new OCSP
+proof. The burden is on the administrator to handle this, outside of
+Exim. The file specified should be replaced atomically, so that the
+contents are always valid. Exim will expand the &%tls_ocsp_file%& option
+on each connection, so a new file will be handled transparently on the
+next connection.
+
+When built with OpenSSL Exim will check for a valid next update timestamp
+in the OCSP proof; if not present, or if the proof has expired, it will be
+ignored.
+
+For the client to be able to verify the stapled OCSP the server must
+also supply, in its stapled information, any intermediate
+certificates for the chain leading to the OCSP proof from the signer
+of the server certificate. There may be zero or one such. These
+intermediate certificates should be added to the server OCSP stapling
+file named by &%tls_ocsp_file%&.
+
+Note that the proof only covers the terminal server certificate,
+not any of the chain from CA to it.
+
+.code
+ A helper script "ocsp_fetch.pl" for fetching a proof from a CA
+ OCSP server is supplied. The server URL may be included in the
+ server certificate, if the CA is helpful.
+
+ One failure mode seen was the OCSP Signer cert expiring before the end
+ of validity of the OCSP proof. The checking done by Exim/OpenSSL
+ noted this as invalid overall, but the re-fetch script did not.
+.endd
+
+
.section "Configuring an Exim client to use TLS" "SECID185"
certificate verification to the listed servers. Verification either must
or need not succeed respectively.
+The &(smtp)& transport has two OCSP-related options:
+&%hosts_require_ocsp%&; a host-list for which a Certificate Status
+is requested and required for the connection to proceed. The default
+value is empty.
+&%hosts_request_ocsp%&; a host-list for which (additionally)
+a Certificate Status is requested (but not necessarily verified). The default
+value is "*" meaning that requests are made unless configured
+otherwise.
+
+The host(s) should also be in &%hosts_require_tls%&, and
+&%tls_verify_certificates%& configured for the transport,
+for OCSP to be relevant.
+
If
&%tls_require_ciphers%& is set on the &(smtp)& transport, it must contain a
list of permitted cipher suites. If either of these checks fails, delivery to
.next
.vindex "&%tls_verify_certificates%&"
&%tls_verify_certificates%&
+.next
+.vindex "&%tls_ocsp_file%&"
+&%tls_verify_certificates%&
.endlist
Great care should be taken to deal with matters of case, various injection
and the &%hosts_try_prdr%& smtp transport option.
This ACL is evaluated after &%acl_smtp_dkim%& but before &%acl_smtp_data%&.
+If the ACL is not defined, processing completes as if
+the feature was not requested by the client.
.section "The QUIT ACL" "SECTQUITACL"
.cindex "QUIT, ACL for"
git://git.exim.org / exim.git / blobdiff