sendmail/features/authinfo

About
The authinfo feature allows external clients to relay mail via sendmail's SMTP by authenticating in various ways by providing a separate user map.

By default, the authinfo database specification is:

hash /etc/mail/authinfo

...where /etc/mail/authinfo contains the user map to be used.

Missing Documentation
The documentation does not seem to explain how to get authentication against an existing user base, the same way that sendmail's IMAP and POP3 work by default.

Links

 * SMTP authentication
 * very brief feature definition