On cPanel servers the default mail program is Exim. Exim will handle anything to do with mail delivery from sending to receiving. Exim writes logs to four files. The Exim log files on cPanel can be used to diagnose almost any email problem. So, If you are looking for cPanel log files check out our guide on log files.
The Exim Mainlog
The Exim Mainlog is probably the most used of the Exim Log Files. It contains all the information for every email sent and received on the server. Are your messages being deferred? If so the Exim Log file will help. In this file, you can search for email addresses. So, if you are trying to send mail to a user and the email is being rejected or returned try to search with grep. replace [email] with the relevant email address.
grep [email] /var/log/exim_mainlog Exim Reject Log
The reject log details all emails that have been rejected due to ACL. Mail blocked by SpamAssassin but also rate-limited emails will be detailed in this file located at /var/log/exim_rejectlog.
So from Manage ACLs in WHM > Exim Configuration > ACL Options.
/var/log/exim_rejectlogExim Mail Log
The Exim Mail Log contains all the login attempts for POP3 and IMAP connections to the server including SpamAssassin scores, fatal errors but also a complete list of transactions. However, GREP can be used to search this file which is located at
/var/log/maillog Exim Panic Log
The Exim Panic Log contains all the most serious errors and should never have any information listed inside it. If the Panic Log has information inside then these need to be addressed as soon as possible as it’s likely your Exim server is either offline or failing to work as it should but, as a last resort to fix most of these issues you could reset Exim from WHM but you would lose any custom configurations.
/var/log/exim_paniclogAnd now you have all the information required to diagnose almost all email issues with Exim. The Exim log files in cPanel are invaluable to server admins, so allowing you to quickly fix issues customers might be seeing with sending and receiving email.
One of the most common issues we see with cPanel servers and Exim is the fact users do not set up rDNS entries. so, rDNS proves you have the right to mail from that domain name. Always ensure you have an rDNS or PTR record setup for your hostname and main domain name. First2Host customers who run an NVMe VPS or Dedicated server can contact the support team who can configure rDNS records for you.
