There is a quote by someone from a time long ago which goes along the
lines of being conservative in what you generate and liberal in what you
receive.
It's from Host Requirements, STD 3, RFC 1123.
In other words, make sure that you follow the specs to the
letter in what you generate, however try to deal with anything reasonable
that you can anticipate being thrown your way.
No, that's *not* what it means. The Robustness Principle does not
justify ad hoc extensions to the specification (for example, sendmail
accepting `RCPT TO:tim(_at_)uunet(_dot_)pipex(_dot_)com'). Study section 1.2.2
of 1123
carefully.
Tim.