I've had our Zimbra server working for quite a few months without a hitch. Over the last month, however, I'm experiencing problems delivering messages to Gmail. After 72 hours, the message fails:
Final-Recipient: rfc822; XXXXXX@gmail.com
Diagnostic-Code: X-Postfix; delivery temporarily suspended: connect to
gmail.com[18.104.22.168]: Connection timed out
Thank you in advance.