Processing email with a server application

Question

I'm afraid this is a very generic question, but unfortunately my question is exactly how to get down to the 'specifics' on this particular issue. Let me be more specific:

I want to create an "email listener" application - something that would run in my server, so that users could send email to a particular address and this application would fetch the email and do something with its contents. In other words, I want to use common e-mail as a method of user input.

You probably know Remember The Milk. It has a feature where you can e-mail tasks to a particular address and it would be added to your task list. I want to know how this is done 'under the hood'.

For answers, general concepts and articles are fine, but you can obviously point to technology-specific resources, as they can be 'reverse-engineered' so the concepts are extracted. Thanks in advance!

Answer 1

Googling for "processing incoming email" actually returns a fair number of relevant results, such as the following (a PHP example):

http://www.evolt.org/incoming_mail_and_php

Answer 2

You can find code that does this inside any mailing list manager or similar application. You could also look inside an SMTP server itself. I recommend you take a look at GNU Mailman, which is a mailing list manager.