Postfix attempts to be fast, easy to administer, and secure, while at the same time being sendmail compatible enough to not upset existing users. Thus, the outside has a sendmail-ish flavor, but the inside is completely different. Some feautures: Connection cache for SMTP, DSN status notifications, IP version 6, Plug-in support for multiple SASL implementations (Cyrus, Dovecot), TLS encryption and authentication, Configurable status notification message text, Access control per client/sender/recipient/etc, Content filter (built-in, external before queue, external after queue), Berkeley DB database, LDAP database, MySQL database, PostgreSQL database, Maildir and mailbox format, Virtual domains, VERP envelope return addresses and others.