No error messages
There are no error messages in my var/log/mail.log file and there is no var/log/mail.err text file generated. BUT, what is curious is that there are no sub-directories for the email accounts in the var/vmail/domain.com and /domain.net directories. Perhaps those folders weren't created because of the missing dependency files? And if those accounts weren't created, why am I able to receive my POP mail and send out via Squirrel Mail?
I'm going to delete those email accounts, then recreate them and let you know what happens.
Thanks, Falko. You're the MAN!!