This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Well, it depends what you want to do when an exception occurs. If in thread 2 you want to notify a user interface of e-mails that didn't get sent, and the user interface is part of thread 1's context, then you should simply pass the user interface to thread 2 when you start it, and let thread 2 deal with the user interface itself.