SASL stands for "Simple Authentication and Security Layer". SASL itself is nothing more than a list of requirements for authentication mechanisms (see [wiki:Authentication Authentication]) and protocols to be SASL-compatible. IMAP, POP3 and SMTP protocols all have support for SASL.
Many people confuse SASL with one specific SASL implementation: the Cyrus SASL library. Dovecot has its own SASL implementation which may at some point be separated from Dovecot itself to "compete" against Cyrus SASL library in server side. And it already can be:
- Latest Postfix development snapshots support Dovecot's SASL server implementation.
There's a [http://www.exim.org/eximwiki/AuthenticatedSmtpUsingDovecot patch for Exim] as well.
Hopefully more software will follow.