I have installed CentOS, LAMP, ISPConfig, etc. All seems OK, SMTP working fine. However... I can't receive any mail. According to ISPConfig the POP3 server is running fine. When I send an email to either wwwX_user@domain.com or firstname.lastname@example.org I get the below error emailed straight back... what am I doing wrong!? This is the mail system at host localhost.localdomain. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to <postmaster> If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <email@example.com> (expanded from <firstname.lastname@example.org>): critical OS file missing. Command output: procmail: Error while writing to "/dev/null" Final-Recipient: rfc822; email@example.com Original-Recipient: rfc822;firstname.lastname@example.org Action: failed Status: 5.3.0 Diagnostic-Code: x-unix; procmail: Error while writing to "/dev/null"