Postfix feature overview
Postfix runs on AIX, BSD, HP-UX, IRIX, LINUX, MacOS X, Solaris, Tru64 UNIX, and other UNIX systems. It requires ANSI C, a POSIX.1 library, and BSD sockets. In addition, Postfix requires that the file system satisfies a number of requirements that are described at the end of this page.
The following is a list of major Postfix features. Some features require third-party libraries (examples: LDAP, SQL, TLS). Other features are available only when the necessary operating system support exists and Postfix knows how to use it (examples: IP version 6, connection caching).
Junk mail control
|Postfix 2.8||Postscreen zombie blocker.|
|Postfix 2.8||DNS whitelist support in smtpd and in postscreen.|
|Postfix 2.5||Stress-dependent configuration|
|Postfix 2.3||Sendmail Milter (mail filter) protocol|
|Postfix 2.2||SMTP server per-client rate and concurrency limits|
|Postfix 2.1||Access control per client/sender/recipient/etc.|
|Postfix 2.1||Address probing callout|
|Postfix 2.1||Greylisting plug-in|
|Postfix 2.1||SPF plug-in|
|Postfix 1.1||Content filter (built-in, external before queue, external after queue)|
|Postfix 2.10||HAproxy support in postscreen and smtpd|
|Postfix 2.9||Nginx proxy support in smtpd including SASL credential passing|
|Postfix 2.3||DKIM, DomainKeys and SenderID authentication (via Milter plug-in)|
|Postfix 2.3||DSN status notifications|
|Postfix 2.3||Enhanced status codes|
|Postfix 2.3||Plug-in support for multiple SASL implementations (Cyrus, Dovecot)|
|Postfix 2.2||Connection cache for SMTP|
|Postfix 2.2||IP version 6|
|Postfix 2.2||TLS encryption and authentication|
|Postfix 2.0||MIME (including 8BITMIME to 7BIT conversion)|
|Postfix 1.0||ETRN on-demand relay|
|Postfix 1.0||LMTP client|
|Postfix 1.0||Pipelining (SMTP client and server)|
|Postfix 1.0||SASL authentication|
|Postfix 1.1||QMQP server|
By popular demand...
|Postfix 2.9||Non-repeating (long) queue IDs|
|Postfix 2.8||Server reject "footer" text|
|Postfix 2.3||Configurable delivery status notification message text|
|Postfix 2.3||Sender-dependent SMTP relay lookup|
|Postfix 2.3||Sender-dependent SASL password lookup|
|Postfix 2.11||LMDB database|
|Postfix 2.10||Sendmail-style socketmap|
|Postfix 2.9||Gradual degradation: many cases a Postfix daemon will log a warning and continue providing the services that are still available, instead of immediately terminating with a fatal error.|
|Postfix 2.9||Memcache database|
|Postfix 2.8||SQLite database|
|Postfix 2.2||CDB database|
|Postfix 2.0||PostgreSQL database|
|Postfix 1.0||LDAP database|
|Postfix 1.0||MySQL database|
|Postfix 1.0||Berkeley DB database|
|Postfix 1.0||DBM database|
|Postfix 1.0||Maildir and mailbox format|
|Postfix 1.0||Virtual domains|
|Postfix 2.2||Masquerading addresses in outbound SMTP mail|
|Postfix 2.2||Selective address rewriting|
|Postfix 1.1||VERP envelope return addresses|
The Postfix mail queue requires that:
Renaming a file to a near-by directory does not change the file's inode number.
A file is not lost after fsync() of that file (not its parent directory) returns successfully, and then the system crashes. This must be true even when that file is later renamed to a near-by directory.
When Postfix in a virtual guest machine flushes a file with fsync(), the file information must not be cached in volatile host memory. Instead the information must immediately be written to disk (or to persistent cache) before fsync() returns in the virtual guest machine.
Postfix can set the execute bit on a queue file. If this does not work, then no mail will ever be delivered.
In addition to the above, Postfix maildir delivery requires that:
A file can be hard linked between different near-by directories.
A file is not lost when it is hard-linked to a near-by directory, unlinked from the old directory, and then the system crashes.
Postfix mailbox delivery introduces no additional requirements.
Files in the Postfix command_directory require that:
The setgid bit works. This is required to access the mail queue with the postdrop command, and to access protected UNIX-domain sockets with the postdrop and postqueue commands.