Comment 4 for bug 810769

+++ This bug was initially created as a clone of Bug #440794 +++

Sending email should use the offline capabilities (dump the mail in Unsent Folders, schedule a background send), so that the user can move on immediately to the next task.

Bug 440794 has done most of the initial work to get basic support, what is left is to be able to manage failures so that send/copy failures are automatically retried, and only notified to the user after several failures, plus the associated UI updates.