What I’m trying to do is figure up how I can configure a mail server such that mails to a specific address will trigger certain actions- e.g. inserting the subject line into a MySQL database, etc. This is for a web app in LAMP- basically I want people to be able to add things automatically via email if they’d rather do that than use the web interface. Kind of like how e.g. with Evernote you can send a mail to your custom address to add a note that way.
I realize this is a pretty vague question, what I’m looking for is a general place to start looking and learning. I’m reasonably familiar with website tech but when it comes to mail servers I’m completely clueless. I’m not looking for any specific implementation: Rather I just want to know what are the basics I need familiarize myself to be able to attack the problem.
If you want to trigger actions “in realtime” you best work with your own mailserver and use something like procmail: Here is an example from the procmail faq how to trigger actions on incoming mails: http://porkmail.org/era/procmail/mini-faq.html#rtfm
But if you can avoid this, just let the fun stuff of mailserver work handle your provider and scan one or more mailboxes via cron-job (on linux/unix) triggered scripts. A cronjob could e.g. be a command line PHP script or a wget script that does a HTTP request on your webserver script to start the action. Your script reads the actual mails via something like http://pear.php.net/manual/en/package.networking.net-pop3.php
(Try to avoid importing the same mail twice e.g. by relying on the message id of the mail or by creating SHA1/MD5 hashes on parts or the body of the mail).
A lot of ticket systems work like this (for example OTRS: http://otrs.org/downloads).