Recently I got very interesting issue and it took very long time to figure our. The problem was I was able to send/receive email to other accounts but not able to send/receive to my own account means firstname.lastname@example.org to email@example.com. Here is what I was getting in error logs (Cpanel server).
gin:firstname.lastname@example.org S=789 email@example.com
2009-04-11 14:20:00 1LsikC-00037z-NP => /dev/null
Then here is what I found in cpanel forums:
central_filter refers to the email filters you’ve set up in cPanel – stored in /etc/vfilters/. Looks like you’ve got a filter set up to drop certain emails.
Then I renamed my domain name files in /etc/vfilters/ and I got this fixed, hope this will help you