We're using Zimbra Open Source Release 6.0.3_GA_1915. Our external smarthost is ExchangeDefender. When sending email, TLS is successful in the SMTP session with ExchangeDefender. Incoming email is received, but uses unencrypted SMTP.

We're using a valid, commercial SSL Certificate from Equifax reflecting the correct, public FQDN of the server.

Any ideas on why TLS works outbound but not inbound? Any help is greatly appreciated in advance.