Postfix

Postfix is an MTA (mail transfer agent) that is intended to be a replacement of the default Sendmail MTA used on many Unix and Unix-like platforms, including FreeBSD. Postfix is considered to be a faster, easier to manage and more secure then Sendmail. It also has the advantage of using the same configuration file options that Sendmail uses to simplify migration and reduce the need to learn a new system.

Origins

Postfix began as a program called VMailer and later became IBM Secure Mailer before being released as Postfix in 1999 under the IBM Public License 1.0. This license makes Postfix free software but is not compatible with the GPL. It continues to be actively developed and has its own website.

Features

Postfix has the following features (references taken from the Wikipedia entry for Postfix).

Storage

Received email can be stored in the following file-based mailboxes

• mbox - a single, flat-file containing all emails addressed to a recipient;
• Maildir - a single directory, usually located under the user's home directory, containing a file per email received;
• virtual domains

Mappings

Mail mapping can be stored in the following database-based formats:

• Berkley DB - a simple but effective database system but does not network;
• CDB - a quick and effective database designed around the file system;
• DBM;
• LDAP - a hierarchical system often used for authentication (Microsoft adapted LDAP to create their Active Directory system);
• MySQL - a real SQL database system similar to Microsoft and Oracle SQL servers;
• PostgreSQL - a real SQL database system similar to Microsoft and Oracle SQL servers.

Security

Security has been enhanced with the following features:

• Transport Layer Security (TLS)
• delegation of SMTP policies to an external process (this allows Greylisting) and advanced content filtering.
• VERP
• SMTP-AUTH via SASL
• Others
• Milter support

One of the strengths of Postfix is its resilience against buffer overflows. Another one is its handling of large amounts of e-mail. Postfix is built as a cooperating network of different daemons. Each daemon fulfills a single task using minimum privileges. In this way, if a daemon is compromised, the impact remains limited to that daemon and cannot spread throughout the entire system. There is only one process with root privileges (master), and a few (local, virtual, pipe) that actually write to disk or invoke external programs. Most daemons can be easily chrooted.

Postfix can also be compiled on AIX, BSD, HP-UX, IRIX, Linux, Mac OS X, Solaris, Tru64 UNIX and, generally speaking, on every Unix-like OS that ships with a C compiler, standard POSIX development libraries and all the libraries required for handling BSD sockets.