I don't think this already exists, if it does could you please point me in the right direction?
I'd like an addon that I can tell to retrieve all of the Frostweave Cloth (for example) out of my mailbox, and have it leave the rest of the items. 
The mail I send my alts becomes very unorganized, 12 attachments in each, all of different catagories.
I find myself sifting through old mail, looking for one type of item at a time, and not wanting all the attachments in my invintory.

Any help? 

Have not seen one that does, but I have not tried them all. 

Postal doesnt do that, it can get only certain types like AH outbids or AH won, but not specific items.