|As of today I'm officially using the Mail3 database for mail storage. It came about primarily because I managed to overwrite one of my Mail2 folders with an empty folder by accident while testing the code that manages folders. (I will make sure that you can't do that before shipping). Anyway seeing as I had to start from scratch, the logical thing to do was dogfood the Mail3 database and get it solid. I know it's like about 4 years after I started talking about it but it's now actually here and stable enough for everyday use. (Which is not to say it's production ready, more like "beta" rather than the previous release being decidedly "alpha")
Currently it's (much?) faster to load than Mail2, has a better memory footprint, but is slower to write to. However I may be able to fix that with better use of transactions. Also there is no easy way to migrate from Mail2 to Mail3, although you can drag and drop between the mail stores while you have both open. Currently the Mail3 format supports Email (duh), Attachments, Contacts and Filters. Support will be added for Calendar Events and Contact Groups shortly.