Why Zimbra Cannot Receive External Mail?

Zimbra is a mail server application. It is open-source mail server having community version and network edition (license version-paid version). Zimbra can be used as the mail server for creating the domain, user, distribution list, managing all mail server activities and sometimes Zimbra cannot receive external mail.

Zimbra provides the ability to have in-house email/calendars/briefcases if your company is required to keep sensitive emails securely within the network.

Administering Zimbra is a bit complicated (dealing with permissions is an utter disaster of undocumented junk), and you can't really avoid the command line (thus paying for a support contract is well worth it).

If you are able to set a standard mailbox for the team, you will be able to access and organize the emails into folders.

Zimbra also allows mobile device access to emails with secure IMAP, which works seamlessly with phones as if it was an Exchange server.

If you are having trouble waiting from the outside, you will need to find out what the error Zimbra cannot receive external mail is caused.

Make sure you check the log files before sending a message, especially a file on the MTA server; /var/log/zimbra.log. This helps to tail the file while sending a message; tail -f /var/log/zimbra.log

To troubleshoot the firewall settings, you should have an account on a system outside the network.

DNS error

The mail domain that your user accounts are created under must have an MX record. To test this: host -t MX domain
If the IP address returned is the public address of MTA, make sure that the Firewall is forwarding port 25 while fixing the error Zimbra cannot receive external mail.