Couple potential snafus here:

- We can learn about new attachments for POP3, so this logic is too guarded here.  It won't do the right thing.

- buildBodyDom is buggy if invoked multiple times (https://bugzilla.mozilla.org/show_bug.cgi?id=912825) and we might need to fix it up a little here.  See the last 2 points in comment 0.