Posting this just in case someone has a similar problem.
Netvanta 7100 in place for several years, upgraded to newer firmware and it stopped sending email for voicemail/logs etc.
7100 is configured to relay through a ubuntu box with postfix, relaying is allowed via ip ranges, so no auth needed. Other than that, the postfix config is default.
Logs on ubuntu box show: lost connection after AUTH
Looks like the newer versions of the Adtran firmware insist on using TLS if the SMTP server says it's available even if the logging email-receiver line does not contain a user or password.
Since I'm not actually using TLS on this postfix box, the simple solution was to change smtpd_use_tls=no in main.cf which made the 7100 happy...
Richard, it sounds like you were running an early version of R10.8, which contained the TLS bug you're describing. Newer versions of code, including the extended maintenance releases of R10.9.6 and R11.4.2 do not contain this particular issue, so an upgrade would allow you to revert the settings in your mail server back to where they were previously. Thanks