Exim
exim is a popular mailserver. You can use the exim command to administer, get info from, and other interactions with the exim mailserver.
exim -Mvh messageID
show email header for the specified message
exim -Mvb messageID (show the body of the email)
exim -Mvl messageID (show the logs for the specified email)
exim -bpc (show the number of e-mails in the queue)
exim -bp (show the e-mails in the queue)
exigrep (grep for mail logs example: exigrep spam@psygen.org /var/log/exim_mainlog )