As I don't use edbrowse as an email client I'm probably not the most qualified
to talk about this side of the code.
However, I would strongly suggest either 2 or 3 as approaches since I think
writing a fully functional imap module is probably going to be a lot of work.

Given how many linux clients support imap (including a very ed-like email
client) I'd be very surprised and disapointed if a decent library isn't
available for this.

Cheers,
Adam.
PS: it looks like edbrowse currently breaks threading,
at least in mutt (probably something to do with message headers)