I recently had to buy an such an add-on (Owl), because my umiversity's IT department killed IMAP support and only offers Exchange (which is stupid, but what can you do?).
Solutions like Owl are actually kind of nice, I have been using a similar one on my phone (AquaMail) for many years and it's worked out great. Thanks for the tip, might give it a shot - I see it's by the same author as ExQuilla which has been around for awhile as well.