I have installed a commercial certificate as described in the wiki and I had the https site and the pop3 access working fine with it, however, when I tried to send mail through smtp, I got "error 454 - TLS not available due to a local problem". I tried settting the certificate for the mta manually by issuing
which installed the original, zimbra issued certificate there. Not happy with that, in a particularly experimental mindset I copied my commercial .crt file over the /opt/zimbra/conf/smtpd.crt file. Now I get the error "unable to connect to smtp server via STARTTLS since it doesn't offer STARTTLS in EHLO response". Not happy with this one either, please help!
zmcertinstall mta ssl/ssl/server/server.crt ssl/ssl/server/server.key