Guide for fix incoming mail from outside problems

When you have problems receiving email from outside, it can be difficult to determine where a message sent to your mail server has gone. First check the mail server logs, which indicate whether the external message has reached the system. Examine /var/log/zimbra.log with this command:

# tail -f /var/log/zimbra.log

Check whether the logs show incoming mail from outside. If they do, the problem may involve incorrect configuration, DNS settings, or firewall settings. Checking DNS and firewall settings

1. DNS Most problems receiving external mail result from incorrect DNS settings. Make sure the MX record is configured correctly. You can use this command:

   # host -t mx domain

   Or:

   # dig -t mx domain

2. Firewall. Check that both the mail server firewall and the system’s firewall gateway allow incoming connections on port 25. Command for checking the mail server firewall:

   # iptables -nL

Checking the internal configuration Check /var/log/zimbra.log for postfix/lmtp … deferred … connection refused. If present, this means the system cannot connect to LMTP on port 7025. Check whether the mail server resolves the mailbox server to the correct IP address. If it does not, set up an internal DNS view for the mail server, or use this command:

# zmlocalconfig -e postfix_lmtp_host_lookup=native

This makes postfix use native lookup, taking data from /etc/hosts instead of looking up DNS. After making the change, remember to restart the service with this command:

# zmmtactl restart

If this still does not resolve the problem, check iptables for any special NAT rules with this command:

# iptables -t nat -nL