- your reverse PTR for Zimbra server's public IP address, which should resolve to main zimbra FQDN or a sub-domain
- Once I had problems with Zimbra' MTA not being authorised, and this command solved the problem:
- did you try sending out to your Gmail or Yahoo mail account? Look at received mail headers, spam score, ham or spam etc. to get some clue
sudo /opt/zimbra/bin/zmprov –m –l yourZimbra.server.com zimbraMtaAuthHost yourZimbra.server.com
- check your Zimbra IP for blacklists. If you are on at least 1 blacklist (except blackscatter, which is not relevant), you might get random delivery rate, depending on how tight recipient's security is.
- do you send mail out directly or smarthost via ISP's SMTP server? If you send out directly, your ISP might have changed security policy and begun blocking port 25 for any mail server, except their own. This was the case with few of our customers.