I installed Zimbra yesterday on a new department mailserver and everything seems to work just fine except for using mail apps to access the SMTP server.

IMAPS works, haven't tried SMTP but in both Apple Mail and Thunderbird the app is not able to connect with our Zimbra box when TLS or SSL is checked, but when I configure the app to send mail without using TLS it does this beautifully.

What do I need to change in the configuraton to enable TLS with the zimbra box?