Best way to automatically archive IMAP email locally?
I've recently switched one of my email accounts from POP to IMAP. Unfortunately, the email provider is VERY stingy with it's mailbox quotas, limiting me to something like 25MB for the inbox and 50MB total (including trash and junk folders). When the total size of messages in my inbox reaches the quota, the oldest are deleted. Not moved to trash, but completely erased. Poof! Gone! This becomes a problem if I receive several large attachments, as I can suddenly find myself with less than a week's worth of emails in my inbox.
This was not a problem when using POP, since everything was saved on my Mac. I prefer to save old messages for at least a year or more for reference purposes, and would like to do so in a local folder in Mail if possible. Now, the trouble is how exactly to go about this in the most automated way possible? My first thought was to create a rule that would copy each message to an archive folder "On My Mac" as they are received. However, it seems that rules are not applied to messages if I first mark them as read from another device (webmail or my iPod touch) then sync Mail on my Mac at a later time. Can anybody suggest a better solution to assure that I can save a copy of all of my mail locally with limited user intervention (I could manually copy each message every day, but that's a pain)?
Macbook Pro, Mac OS X (10.6.6), Apple Mail 4.4 (1082)