Specification of the Exim Mail Transfer Agent

Table of Contents

1. Introduction

1.1. Exim documentation

1.2. FTP and web sites

1.3. Mailing lists

1.4. Exim training

1.5. Bug reports

1.6. Where to find the Exim distribution

1.7. Wish list

1.8. Contributed material

1.9. Limitations

1.10. Run time configuration

1.11. Calling interface

1.12. Terminology

2. Incorporated code

3. How Exim receives and delivers mail

3.1. Overall philosophy

3.2. Policy control

3.3. User filters

3.4. Message identification

3.5. Receiving mail

3.6. Handling an incoming message

3.7. Life of a message

3.8. Processing an address for delivery

3.9. Processing an address for verification

3.10. Running an individual router

3.11. Duplicate addresses

3.12. Router preconditions

3.13. Delivery in detail

3.14. Retry mechanism

3.15. Temporary delivery failure

3.16. Permanent delivery failure

3.17. Failures to deliver bounce messages

4. Building and installing Exim

4.1. Unpacking

4.2. Multiple machine architectures and operating systems

4.3. DBM libraries

4.4. Pre-building configuration

4.5. Support for iconv()

4.6. Including TLS/SSL encryption support

4.7. Use of tcpwrappers

4.8. Including support for IPv6

4.9. The building process

4.10. Output from “ make ”

4.11. Overriding build-time options for Exim

4.12. OS-specific header files

4.13. Overriding build-time options for the monitor

4.14. Installing Exim binaries and scripts

4.15. Installing info documentation

4.16. Setting up the spool directory

4.17. Testing

4.18. Replacing another MTA with Exim

4.19. Upgrading Exim

4.20. Stopping the Exim daemon on Solaris

5. The Exim command line

5.1. Setting options by program name

5.2. Trusted and admin users

5.3. Command line options

6. The Exim run time configuration file

6.1. Using a different configuration file

6.2. Configuration file format

6.3. File inclusions in the configuration file

6.4. Macros in the configuration file

6.5. Macro substitution

6.6. Redefining macros

6.7. Overriding macro values

6.8. Example of macro usage

6.9. Conditional skips in the configuration file

6.10. Common option syntax

6.11. Boolean options

6.12. Integer values

6.13. Octal integer values

6.14. Fixed point number values

6.15. Time interval values

6.16. String values

6.17. Expanded strings

6.18. User and group names

6.19. List construction

6.20. Empty items in lists

6.21. Format of driver configurations

7. The default configuration file

7.1. Main configuration settings

7.2. ACL configuration

7.3. Router configuration

7.4. Transport configuration

7.5. Default retry rule

7.6. Rewriting configuration

7.7. Authenticators configuration

8. Regular expressions

8.1. Testing regular expressions

9. File and database lookups

9.1. Examples of different lookup syntax

9.2. Lookup types

9.3. Single-key lookup types

9.4. Query-style lookup types

9.5. Temporary errors in lookups

9.6. Default values in single-key lookups

9.7. Partial matching in single-key lookups

9.8. Lookup caching

9.9. Quoting lookup data

9.10. More about dnsdb

9.11. Pseudo dnsdb record types

9.12. Multiple dnsdb lookups

9.13. More about LDAP

9.14. Format of LDAP queries

9.15. LDAP quoting

9.16. LDAP connections

9.17. LDAP authentication and control information

9.18. Format of data returned by LDAP

9.19. More about NIS+

9.20. SQL lookups

9.21. More about MySQL, PostgreSQL, Oracle, and Interbase

9.22. Special MySQL features

9.23. Special PostgreSQL features

9.24. More about SQLite

10. Domain, host, address, and local part lists

10.1. Expansion of lists

10.2. Negated items in lists

10.3. File names in lists

10.4. An lsearch file is not an out-of-line list

10.5. Named lists

10.6. Named lists compared with macros

10.7. Named list caching

10.8. Domain lists

10.9. Host lists

10.10. Special host list patterns

10.11. Host list patterns that match by IP address

10.12. Host list patterns for single-key lookups by host address

10.13. Host list patterns that match by host name

10.14. Behaviour when an IP address or name cannot be found

10.15. Host list patterns for single-key lookups by host name

10.16. Host list patterns for query-style lookups

10.17. Mixing wildcarded host names and addresses in host lists

10.18. Address lists

10.19. Case of letters in address lists

10.20. Local part lists

11. String expansions

11.1. Literal text in expanded strings

11.2. Character escape sequences in expanded strings

11.3. Testing string expansions

11.4. Forced expansion failure

11.5. Expansion items

11.6. Expansion operators

11.7. Expansion conditions

11.8. Combining expansion conditions

11.9. Expansion variables

12. Embedded Perl

12.1. Setting up so Perl can be used

12.2. Calling Perl subroutines

12.3. Calling Exim functions from Perl

12.4. Use of standard output and error by Perl

13. Starting the daemon and the use of network interfaces

13.1. Starting a listening daemon

13.2. Special IP listening addresses

13.3. Overriding local_interfaces and daemon_smtp_ports

13.4. Support for the obsolete SSMTP (or SMTPS) protocol

13.5. IPv6 address scopes

13.6. Examples of starting a listening daemon

13.7. Recognising the local host

13.8. Delivering to a remote host

14. Main configuration

14.1. Miscellaneous

14.2. Exim parameters

14.3. Privilege controls

14.4. Logging

14.5. Frozen messages

14.6. Data lookups

14.7. Message ids

14.8. Embedded Perl Startup

14.9. Daemon

14.10. Resource control

14.11. Policy controls

14.12. Callout cache

14.13. TLS

14.14. Local user handling

14.15. All incoming messages (SMTP and non-SMTP)

14.16. Non-SMTP incoming messages

14.17. Incoming SMTP messages

14.18. SMTP extensions

14.19. Processing messages

14.20. System filter

14.21. Routing and delivery

14.22. Bounce and warning messages

14.23. Alphabetical list of main options

15. Generic options for routers

16. The accept router

17. The dnslookup router

17.1. Problems with DNS lookups

17.2. Private options for dnslookup

17.3. Effect of qualify_single and search_parents

18. The ipliteral router

19. The iplookup router

20. The manualroute router

20.1. Private options for manualroute

20.2. Routing rules in route_list

20.3. Routing rules in route_data

20.4. Format of the list of hosts

20.5. Format of one host item

20.6. How the list of hosts is used

20.7. How the options are used

20.8. Manualroute examples

21. The queryprogram router

22. The redirect router

22.1. Redirection data

22.2. Forward files and address verification

22.3. Interpreting redirection data

22.4. Items in a non-filter redirection list

22.5. Redirecting to a local mailbox

22.6. Special items in redirection lists

22.7. Duplicate addresses

22.8. Repeated redirection expansion

22.9. Errors in redirection lists

22.10. Private options for the redirect router

23. Environment for running local transports

23.1. Concurrent deliveries

23.2. Uids and gids

23.3. Current and home directories

23.4. Expansion variables derived from the address

24. Generic options for transports

25. Address batching in local transports

26. The appendfile transport

26.1. The file and directory options

26.2. Private options for appendfile

26.3. Operational details for appending

26.4. Operational details for delivery to a new file

26.5. Maildir delivery

26.6. Using tags to record message sizes

26.7. Using a maildirsize file

26.8. Mailstore delivery

26.9. Non-special new file delivery

27. The autoreply transport

27.1. Private options for autoreply

28. The lmtp transport

29. The pipe transport

29.1. Concurrent delivery

29.2. Returned status and data

29.3. How the command is run

29.4. Environment variables

29.5. Private options for pipe

29.6. Using an external local delivery agent

30. The smtp transport

30.1. Multiple messages on a single connection

30.2. Use of the $host variable

30.3. Private options for smtp

30.4. How the limits for the number of hosts to try are used

31. Address rewriting

31.1. Explicitly configured address rewriting

31.2. When does rewriting happen?

31.3. Testing the rewriting rules that apply on input

31.4. Rewriting rules

31.5. Rewriting patterns

31.6. Rewriting replacements

31.7. Rewriting flags

31.8. Flags specifying which headers and envelope addresses to rewrite

31.9. The SMTP-time rewriting flag

31.10. Flags controlling the rewriting process

31.11. Rewriting examples

32. Retry configuration

32.1. Retry rules

32.2. Choosing which retry rule to use for address errors

32.3. Choosing which retry rule to use for host errors

32.4. Retry rules for specific errors

32.5. Retry rules for specified senders

32.6. Retry parameters

32.7. Retry rule examples

32.8. Timeout of retry data

32.9. Long-term failures

32.10. Ultimate address timeout

33. SMTP authentication

33.1. Generic options for authenticators

33.2. The AUTH parameter on MAIL commands

33.3. Authentication on an Exim server

33.4. Testing server authentication

33.5. Authentication by an Exim client

34. The plaintext authenticator

34.1. Using plaintext in a server

34.2. The PLAIN authentication mechanism

34.3. The LOGIN authentication mechanism

34.4. Support for different kinds of authentication

34.5. Using plaintext in a client

35. The cram_md5 authenticator

35.1. Using cram_md5 as a server

35.2. Using cram_md5 as a client

36. The cyrus_sasl authenticator

36.1. Using cyrus_sasl as a server

37. The spa authenticator

37.1. Using spa as a server

37.2. Using spa as a client

38. Encrypted SMTP connections using TLS/SSL

38.1. Support for the legacy “ ssmtp ” (aka “ smtps ”) protocol

38.2. OpenSSL vs GnuTLS

38.3. GnuTLS parameter computation

38.4. Requiring specific ciphers in OpenSSL

38.5. Requiring specific ciphers in GnuTLS

38.6. Configuring an Exim server to use TLS

38.7. Requesting and verifying client certificates

38.8. Revoked certificates

38.9. Configuring an Exim client to use TLS

38.10. Multiple messages on the same encrypted TCP/IP connection

38.11. Certificates and all that

38.12. Certificate chains

38.13. Self-signed certificates

39. Access control lists

39.1. Testing ACLs

39.2. Specifying when ACLs are used

39.3. The non-SMTP ACL

39.4. The connect ACL

39.5. The DATA ACLs

39.6. The MIME ACL

39.7. The QUIT ACL

39.8. Finding an ACL to use

39.9. ACL return codes

39.10. Unset ACL options

39.11. Data for message ACLs

39.12. Data for non-message ACLs

39.13. Format of an ACL

39.14. ACL verbs

39.15. ACL variables

39.16. Condition and modifier processing

39.17. ACL modifiers

39.18. Use of the control modifier

39.19. Adding header lines with the warn verb

39.20. ACL conditions

39.21. Using DNS lists

39.22. Specifying the IP address for a DNS list lookup

39.23. DNS lists keyed on domain names

39.24. Multiple explicit keys for a DNS list

39.25. Data returned by DNS lists

39.26. Variables set from DNS lists

39.27. Additional matching conditions for DNS lists

39.28. Negated DNS matching conditions

39.29. DNS lists and IPv6

39.30. Rate limiting senders

39.31. Address verification

39.32. Callout verification

39.33. Additional parameters for callouts

39.34. Callout caching

39.35. Sender address verification reporting

39.36. Redirection while verifying

39.37. Client SMTP authorization (CSA)

39.38. Bounce address tag validation

39.39. Using an ACL to control relaying

39.40. Checking a relay configuration

40. Content scanning at ACL time

40.1. Scanning for viruses

40.2. Scanning with SpamAssassin

40.3. Calling SpamAssassin from an Exim ACL

40.4. Scanning MIME parts

40.5. Scanning with regular expressions

40.6. The demime condition

41. Adding a local scan function to Exim

41.1. Building Exim to use a local scan function

41.2. API for local_scan()

41.3. Configuration options for local_scan()

41.4. Available Exim variables

41.5. Structure of header lines

41.6. Structure of recipient items

41.7. Available Exim functions

41.8. More about Exim’s memory handling

42. System-wide message filtering

42.1. Specifying a system filter

42.2. Testing a system filter

42.3. Contents of a system filter

42.4. Additional variable for system filters

42.5. Defer, freeze, and fail commands for system filters

42.6. Adding and removing headers in a system filter

42.7. Setting an errors address in a system filter

42.8. Per-address filtering

43. Message processing

43.1. Submission mode for non-local messages

43.2. Line endings

43.3. Unqualified addresses

43.4. The UUCP From line

43.5. Resent- header lines

43.6. The Auto-Submitted: header line

43.7. The Bcc: header line

43.8. The Date: header line

43.9. The Delivery-date: header line

43.10. The Envelope-to: header line

43.11. The From: header line

43.12. The Message-ID: header line

43.13. The Received: header line

43.14. The Return-path: header line

43.15. The Sender: header line

43.16. Adding and removing header lines in routers and transports

43.17. Constructed addresses

43.18. Case of local parts

43.19. Dots in local parts

43.20. Rewriting addresses

44. SMTP processing

44.1. Outgoing SMTP and LMTP over TCP/IP

44.2. Errors in outgoing SMTP

44.3. Variable Envelope Return Paths (VERP)

44.4. Incoming SMTP messages over TCP/IP

44.5. Unrecognized SMTP commands

44.6. Syntax and protocol errors in SMTP commands

44.7. Use of non-mail SMTP commands

44.8. The VRFY and EXPN commands

44.9. The ETRN command

44.10. Incoming local SMTP

44.11. Outgoing batched SMTP

44.12. Incoming batched SMTP

45. Customizing bounce and warning messages

45.1. Customizing bounce messages

45.2. Customizing warning messages

46. Some common configuration settings

46.1. Sending mail to a smart host

46.2. Using Exim to handle mailing lists

46.3. Syntax errors in mailing lists

46.4. Re-expansion of mailing lists

46.5. Closed mailing lists

46.6. Virtual domains

46.7. Multiple user mailboxes

46.8. Simplified vacation processing

46.9. Taking copies of mail

46.10. Intermittently connected hosts

46.11. Exim on the upstream server host

46.12. Exim on the intermittently connected client host

47. Using Exim as a non-queueing client

48. Log files

48.1. Where the logs are written

48.2. Logging to local files that are periodically “ cycled ”

48.3. Datestamped log files

48.4. Logging to syslog

48.5. Log line flags

48.6. Logging message reception

48.7. Logging deliveries

48.8. Discarded deliveries

48.9. Deferred deliveries

48.10. Delivery failures

48.11. Fake deliveries

48.12. Completion

48.13. Summary of Fields in Log Lines

48.14. Other log entries

48.15. Reducing or increasing what is logged

48.16. Message log

49. Exim utilities

49.1. Finding out what Exim processes are doing (exiwhat)

49.2. Selective queue listing (exiqgrep)

49.3. Summarising the queue (exiqsumm)

49.4. Extracting specific information from the log (exigrep)

49.5. Selecting messages by various criteria (exipick)

49.6. Cycling log files (exicyclog)

49.7. Mail statistics (eximstats)

49.8. Checking access policy (exim_checkaccess)

49.9. Making DBM files (exim_dbmbuild)

49.10. Finding individual retry times (exinext)

49.11. Hints database maintenance (exim_dumpdb, exim_fixdb, exim_tidydb)

49.12. exim_dumpdb

49.13. exim_tidydb

49.14. exim_fixdb

49.15. Mailbox maintenance (exim_lock)

50. The Exim monitor

50.1. Running the monitor

50.2. The stripcharts

50.3. Main action buttons

50.4. The log display

50.5. The queue display

50.6. The queue menu

51. Security considerations

51.1. Building a more “ hardened ” Exim

51.2. Root privilege

51.3. Running Exim without privilege

51.4. Delivering to local files

51.5. IPv4 source routing

51.6. The VRFY, EXPN, and ETRN commands in SMTP

51.7. Privileged users

51.8. Spool files

51.9. Use of argv[0]

51.10. Use of %f formatting

51.11. Embedded Exim path

51.12. Use of sprintf()

51.13. Use of debug_printf() and log_write()

51.14. Use of strcat() and strcpy()

52. Format of spool files

52.1. Format of the -H file

53. Adding new drivers or lookup types

Index