- (2) The caching arrangements for postmaster checking do NOT take account of
- the sender address. It is assumed that either the empty address, or a
- fixed non-empty address will be used. All that Exim remembers is that
- the postmaster check for the domain succeeded or failed.
-
- 7. When verifying addresses in header lines using the verify=header_sender
- option, Exim behaves by default as if the addresses are envelope sender
- addresses from a message. Callout verification therefore tests to see
- whether a bounce message could be delivered, by using an empty address in
- the MAIL FROM command. However, it is arguable that these addresses might
- never be used as envelope senders, and could therefore justifiably reject
- bounce messages (empty senders). There is now an additional callout option
- for verify=header_sender that allows you to specify what address to use in
- the MAIL FROM command. You use it as in this example:
-
- require verify = header_sender/callout=mailfrom=abcd@x.y.z
-
- Important notes:
-
- (1) As in the case of postmaster_mailfrom (see above), you should think
- about possible loops.
-
- (2) In this case, as in the case of recipient callouts with non-empty
- senders (the use_sender option), caching is done on the basis of a
- recipient/sender pair.
-
- 8. If you build Exim with USE_READLINE=yes in Local/Makefile, it will try to
- load libreadline dynamically whenever the -be (test expansion) option is
- used without command line arguments. If successful, it will then use
- readline() for reading the test data. A line history is supported. By the
- time Exim does this, it is running as the calling user, so this should not
- cause any security problems. Security is the reason why this is NOT
- supported for -bt or -bv, when Exim is running as root or exim,
- respectively. Note that this option adds to the size of the Exim binary,
- because the dynamic loading library is not otherwise included. On my
- desktop it adds about 2.5K. You may need to add -ldl to EXTRA_LIBS when you
- set USE_READLINE=yes.
-
- 9. Added ${str2b64:<string>} to the expansion operators. This operator
- converts an arbitrary string into one that is base64 encoded.
-
-10. A new authenticator, called cyrus_sasl, has been added. This requires
- the presence of the Cyrus SASL library; it authenticates by calling this
- library, which supports a number of authentication mechanisms, including
- PLAIN and LOGIN, but also several others that Exim does not support
- directly. The code for this authenticator was provided by Matthew
- Byng-Maddick of A L Digital Ltd (http://www.aldigital.co.uk). Here follows
- draft documentation:
-
- xx. THE CYRUS_SASL AUTHENTICATOR
-
- The cyrus_sasl authenticator provides server support for the Cyrus library
- Implementation of the RFC 2222 "Simple Authentication and Security Layer".
- It provides a gatewaying mechanism directly to the Cyrus interface, so if
- your Cyrus library can do, for example, CRAM-MD5, then so can the
- cyrus_sasl authenticator. By default it uses the public name of the driver
- to determine which mechanism to support.
-
- Where access to some kind of secret file is required, for example in GSSAPI
- or CRAM-MD5, it is worth noting that the authenticator runs as the exim
- user, and that the Cyrus SASL library has no way of escalating privileges
- by default. You may also find you need to set environment variables,
- depending on the driver you are using.
-
- xx.1 Using cyrus_sasl as a server
-
- The cyrus_sasl authenticator has four private options. It puts the username
- (on a successful authentication) into $1.
-
- server_hostname Type: string* Default: $primary_hostname
-
- This option selects the hostname that is used when communicating with
- the library. It is up to the underlying SASL plug-in what it does with
- this data.
-
- server_mech Type: string Default: public_name
-
- This option selects the authentication mechanism this driver should
- use. It allows you to use a different underlying mechanism from the
- advertised name. For example:
-
- sasl:
- driver = cyrus_sasl
- public_name = X-ANYTHING
- server_mech = CRAM-MD5
- server_set_id = $1
-
- server_realm Type: string Default: unset
-
- This is the SASL realm that the server is claiming to be in.
-
- server_service Type: string Default: "smtp"
-
- This is the SASL service that the server claims to implement.
-
- For straigthforward cases, you do not need to set any of the
- authenticator's private options. All you need to do is to specify an
- appropriate mechanism as the public name. Thus, if you have a SASL library
- that supports CRAM-MD5 and PLAIN, you might have two authenticators as
- follows:
-
- sasl_cram_md5:
- driver = cyrus_sasl
- public_name = CRAM-MD5
- server_set_id = $1
-
- sasl_plain:
- driver = cyrus_sasl
- public_name = PLAIN
- server_set_id = $1
-
-11. There is a new global option called tls_on_connect_ports. Its value must be
- a list of port numbers; the most common use is expected to be
-
- tls_on_connect_ports = 465
-
- Setting this option has the same effect as -tls-on-connect on the command
- line, but only for the specified ports. It applies to all connections, both
- via the daemon and via inetd. You still need to specify all the ports for
- the daemon (using daemon_smtp_ports or local_interfaces or the -X command
- line option) because this option does not add an extra port -- rather, it
- specifies different behaviour on a port that is defined elsewhere. The
- -tls-on-connect command line option overrides tls_on_connect_ports, and
- forces tls-on-connect for all ports.
-
-12. There is a new ACL that is run when a DATA command is received, before the
- data itself is received. The ACL is defined by acl_smtp_predata. (Compare
- acl_smtp_data, which is run after the data has been received.)
- This new ACL allows a negative response to be given to the DATA command
- itself. Header lines added by MAIL or RCPT ACLs are not visible at this
- time, but any that are defined here are visible when the acl_smtp_data ACL
- is run.
-
-13. The "control=submission" ACL modifier has an option "/domain=xxx" which
- specifies the domain to be used when creating From: or Sender: lines using
- the authenticated id as a local part. If the option is supplied with an
- empty domain, that is, just "/domain=", Exim assumes that the authenticated
- id is a complete email address, and it uses it as is when creating From:
- or Sender: lines.
-
-14. It is now possible to make retry rules that apply only when the failing
- message has a specific sender. In particular, this can be used to define
- retry rules that apply only to bounce messages. The syntax is to add a new
- third item to a retry rule, of the form "senders=<address list>". The retry
- timings themselves then become the fourth item. For example:
-
- * * senders=: F,1h,30m
-
- would match all bounce messages. If the address list contains white space,
- it must be enclosed in quotes. For example:
-
- a.domain timeout senders="x@b.dom : y@c.dom" G,8h,10m,1.5
-
- When testing retry rules using -brt, you can supply a sender using the -f
- command line option, like this:
-
- exim -f "" -brt user@dom.ain
-
- If you do not set -f with -brt, a retry rule that contains a senders list
- will never be matched.
-
-15. Two new control modifiers have been added to ACLs: "control = enforce_sync"
- and "control = no_enforce_sync". This makes it possible to be selective
- about when SMTP synchronization is enforced. The global option
- smtp_enforce_sync now specifies the default state of the switch. These
- controls can appear in any ACL, but the most obvious place to put them is
- in the ACL defined by acl_smtp_connect, which is run at the start of an
- incoming SMTP connection, before the first synchronization check.
-
-16. Another two new control modifiers are "control = caseful_local_part" and
- "control = caselower_local_part". These are permitted only in the ACL
- specified by acl_smtp_rcpt (i.e. during RCPT processing). By default, the
- contents of $local_part are lower cased before ACL processing.
- After "control = caseful_local_part", any uppercase letters in the original
- local part are restored in $local_part for the rest of the ACL, or until
- "control = caselower_local_part" is encountered. However, this applies only
- to local part handling that takes place directly in the ACL (for example,
- as a key in lookups). If a "verify = recipient" test is obeyed, the
- case-related handling of the local part during the verification is
- controlled by the router configuration (see the caseful_local_part generic
- router option).
-
- This facility could be used, for example, to add a spam score to local
- parts containing upper case letters. For example, using $acl_m4 to
- accumulate the spam score:
-
- warn control = caseful_local_part
- set acl_m4 = ${eval:\
- $acl_m4 + \
- ${if match{$local_part}{[A-Z]}{1}{0}}\
- }
- control = caselower_local_part
-
- Notice that we put back the lower cased version afterwards, assuming that
- is what is wanted for subsequent tests.
-
-17. The option hosts_connection_nolog is provided so that certain hosts can be
- excepted from logging when the +smtp_connection log selector is set. For
- example, you might want not to log SMTP connections from local processes,
- or from 127.0.0.1, or from your local LAN. The option is a host list with
- an unset default. Because it is consulted in the main loop of the daemon,
- you should strive to restrict its value to a short inline list of IP
- addresses and networks. To disable logging SMTP connections from local
- processes, you must create a host list with an empty item. For example:
-
- hosts_connection_nolog = :
-
- If the +smtp_connection log selector is not set, this option has no effect.
-
-18. There is now an acl called acl_smtp_quit, which is run for the QUIT
- command. The outcome of the ACL does not affect the response code to QUIT,
- which is always 221. Thus, the ACL does not in fact control any access.
- For this reason, the only verbs that are permitted are "accept" and "warn".
-
- The ACL can be used for tasks such as custom logging at the end of an SMTP
- session. For example, you can use ACL variables in other ACLs to count
- messages, recipients, etc., and log the totals at QUIT time using one or
- more "logwrite" modifiers on a "warn" command.
-
- You do not need to have a final "accept", but if you do, you can use a
- "message" modifier to specify custom text that is sent as part of the 221
- response.
-
- This ACL is run only for a "normal" QUIT. For certain kinds of disastrous
- failure (for example, failure to open a log file, or when Exim is bombing
- out because it has detected an unrecoverable error), all SMTP commands
- from the client are given temporary error responses until QUIT is received
- or the connection is closed. In these special cases, the ACL is not run.
-
-19. The appendfile transport has two new options, mailbox_size and mailbox_
- filecount. If either these options are set, it is expanded, and the result
- is taken as the current size of the mailbox or the number of files in the
- mailbox, respectively. This makes it possible to use some external means of
- maintaining the data about the size of a mailbox for enforcing quota
- limits. The result of expanding these option values must be a decimal
- number, optionally followed by "K" or "M".
-
-20. It seems that there are broken clients in use that cannot handle multiline
- SMTP responses. Can't people who implement these braindead programs read?
- RFC 821 mentions multiline responses, and it is over 20 years old. They
- must handle multiline responses for EHLO, or do they still use HELO?
- Anyway, here is YAWFAB (yet another workaround for asinine brokenness).
- There's a new ACL switch that can be set by
-
- control = no_multiline_responses
-
- If this is set, it suppresses multiline SMTP responses from ACL rejections.
- One way of doing this would have been just to put out these responses as
- one long line. However, RFC 2821 specifies a maximum of 512 bytes per
- response ("use multiline responses for more" it says), and some of the
- responses might get close to that. So I have implemented this by doing two
- very easy things:
-
- (1) Extra information that is normally output as part of a rejection
- caused by sender verification failure is omitted. Only the final line
- (typically "sender verification failed") is now sent.
-
- (2) If a "message" modifier supplies a multiline response, only the first
- line is output.
-
- The setting of the switch can, of course, be made conditional on the
- calling host.
-
-21. There is now support for the libradius library that comes with FreeBSD.
- This is an alternative to the radiusclient library that Exim already
- supports. To use the FreeBSD library, you need to set
-
- RADIUS_LIB_TYPE=RADLIB
-
- in Local/Makefile, in addition to RADIUS_CONFIGURE_FILE, and you probably
- also need -libradius in EXTRALIBS.
-
-
-Version 4.42
git://git.exim.org / exim.git / blobdiff