Hmm... are user accounts on this server accessed via LDAP or the local users file? It looks like when Zimbra tries to open a ssh connection to itself it is getting an access denied by your PAM configuration.
Try running this command as the zimbra user and see what you get. It should look like this:
Code:
zimbra@email:~$ ssh -p 12345 -i /opt/zimbra/.ssh/zimbra_identity localhost
The authenticity of host '[localhost]:12345 ([127.0.0.1]:12345)' can't be established.
RSA key fingerprint is 95:fa:10:74:ee:58:2f:56:03:f9:4c:85:cd:d8:f1:89.
Are you sure you want to continue connecting (yes/no)?
Also... looks like we both forgot that you already posted your /var/log/secure.log
right here 