Haha, thanks for your frank words. I actually like your idea for 2 reasons:

1) OpenSource would definitely improve the quality of the app while still maintaining a way to profit from my work.

2) Finally giving back to OpenSource. Always felt kinda bad I haven't contributed much to a great community.

There is definatly a lot of service you could provide even if the app is open source. As GP said, hosting and infrastructure, but also better spam filtering, taking not get and remove domains from spam lists (SPF, DomainKeys, checking your domain and custom domains against spam lists and notifying the owner, &c).

Also, a nice export to S3 or a tar.gz or something would be nice if you were a private service.

I already backup all incoming mail as JSON on my Dropbox and plan to do the same periodically as MBOX. I'm not entirely sure what to do with the JSON, though. It's a "leftover" from my first prototype, where I stored ALL DATA on Dropbox.

Agreed, I'd also be running this immediately if it was open source.

completely agree. I think if you were to open source this and did it right you could get an enormous community behind it.