[exim] Mail Purge

Folks,

We need to write a script to auto purge mail after x days - we are using Exim 4 with the maildir format.

I want to make sure we handle any directories the user might make on the server via IMAP or webmail but at the same time I don't want to risk deleting something I shouldn't.

Right now on my current install I see 2 directories I should NOT process

courierimapkeywords
tmp

My question is am I safe to just skip these 2 directories or is there a better way? For example is there some way I can process every directory and determine if the file I'm looking at is a mail file (and not something else)?

Or would it be valid to say the only mail directories under a user's account is either called "cur" or starts with a period ".someotherfolder"?

Any advise would be appreciated.

TIA!