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.

Extra features always included:

- table lookups using PCRE (Perl-Compatible Regular Expression)

Optional features included using flavors:

- authenticated SMTP using Cyrus SASL v2
- table lookups using LDAP, MySQL and PostgreSQL
