Newbie why is dovecot classified diff then sendmail or courier

Hello, this is probably a dumb question, but I can't for the life of me figure out why sendmail and courier are classified universally as network-mail-mta whereas dovecot is in places like network-mail-general or some such place. I've used several Linux distros and have noted this keenly (they also normally classify photorec, the HD recovery tool as hardware-photography,so this may just be a mistake). I'm concerned that I'm looking into the wrong software for an mail transport/delivery agent.

Thanks, David