53 on a standart Debian install you can read "mail" that got onto your system. The project I work on needs to send an activation link when you made an account. I haven't hooked this up yet to a real mail server as I am lazy thus it uses the mail system from debian to "send" mails. Obviously they can only stay at localhost and the thing before the @ is equal to the user name.
Another thing is that I often work remotely on school projects when I am home as the project is already stored on my laptop (due to me working on them at school). This way I don't need to copy the database and files over to my desktop and back each time I need to switch from computer. This is done very easily as the filemanager I use can mount sftp-servers as pretty much normal drives allowing almost every application I use to work with said server.
The derp I made was that I was using mutt to check for the mail it should have send on my desktop, instead on my laptop which was supposed to send it to localhost. So...the program worked, I was just looking at the wrong computer >_>