[IMP] [WIP] mail: Set an OpenERP alias as the bounce address.

Attempts to fix issue #3347.

This makes OpenERP 7.0 issue a SMTP MAIL FROM command with an address it "owns".
Sorry what I meant in my previous comment is that we should not bother with "fuzzy" cases. Either the admin has configured a catchall domain (or alias), and we use it, or she hasn't, and we keep the previous behavior. Whoever doesn't care enough to set it properly doesn't care about the consequences of not setting it, and the previous behavior is good enough for them.