Sieve

     Sieve is a language used to write filters that are applied on an IMAP server when mail is delivered to an account on that IMAP server.  Being server-side, it allows you to define your filtering scripts once, and have them applied to your e-mail regardless oh how that account is accessed.  Information on writing sieve scripts isn't exactly common; information is out there, but you have to do a good deal of digging.  Here are some of the links I found useful.

• Fastmail is an e-mail hosting provider (I do not use them), and has a good deal of very useful information.

     I'm still looking for a way to get scripts onto the IMAP server and compiled;  I still haven't found documentation addressing this directly.  For now, I'm using SquirrelMail's AlviSieve plugin.  It's the only thing I use SquirrelMail for.