Hard to advise without more info - best guess would be server problem
without anything else. If Tbird has a problem with authentication, it
should not be intermittent - it would be all the time.
Who is your ISP?
Do they require secure connections?
Look under Account Settings, far left column, very bottom choice of
Outgoing Server (SMTP)
Do you have more than one listed?
An authentication problem can cause the loss of your saved user ID and
password for that account. See bug #437930 at
<https://bugzilla.mozilla.org/show_bug.cgi?id=437930>.
--
David E. Ross
<http://www.rossde.com/>
On occasion, I might filter and ignore all newsgroup messages
posted through GoogleGroups via Google's G2/1.0 user agent
because of spam from that source.