Postfix is an open source and free command-line software project implemented in C and designed from the ground up to act as a mailer server for GNU/Linux and UNIX-like operating systems. It is engineered as a Sendmail alternative.
Offers attractive junk mail control features
Junk mail control features include support for the Sendmail Milter (mail filter) protocol, stress-dependent configuration, postscreen zombie blocker, Greylisting plugin, address probing callout, access control per recipient, sender or client, SPF plugin, content filter, DNS whitelist support, as well as SMTP server per-client concurrency and rate limits.
Supports a wide range of protocols
The software supports a wide range of protocols, among which we can mention IPv6, TLS (Transport Layer Security), SMTP (Simple Mail Transfer Protocol), LMTP (Local Mail Transfer Protocol), QMQP (Quick Mail Queueing Protocol), SASL (Simple Authentication and Security Layer), and ETRN (Extended SMTP).
Supported databases and mailboxes
Postfix offers support for several databases, including LMDB database, Memcache database, CDB database, PostgreSQL database, SQLite database, Postfix 1.0 LDAP database, Berkeley DB database, MySQL database, as well as DBM database. In addition, it comes with support for various mailboxes, including the widely used mailbox and maildir formats, and virtual domains.
Supports sender-dependent SMTP relay and SASL password lookup
Among other features, we can mention support for VERP envelope return addresses, masquerading addresses in outbound SMTP mail, selective address rewriting, non-repeating queue IDs, sender-dependent SMTP relay and SASL password lookup, customizable delivery status notification message text, and server reject "footer" text.
Supported operating systems
Postfix is a true cross-platform project that has been successfully tested on a wide range of POSIX operating systems, such as GNU/Linux, BSD, Solaris, AIX, HP-UX, IRIX, Mac OS X and Tru64 UNIX. It is compatible with both 32-bit and 64-bit CPU architectures and it is successfully used on numerous hosting services.