My Zimbra is 7.1.4, all working fine with SMTPS/SSL/465 and POP3S/SSL/995, and webmail ou clients (Thunderbird/Outlook).
Now, I have some shell scripts that run all nights and send automatic emails.
Before Zimbra, I used mailx with postfix like this:
cat somefile | mailx -s "SOMETITLE" someemail@mydomain
I tried the same command in my server running Zimbra. No errors arise in prompt but none email is sent.