Your problem might be with the @yahoo.com email address you're using. Gmail really upped the bar with its spam protection and other email services have been trying to play catch-up for a while. One of the things they have been doing is aggressively blocking auto-generated emails-- like the ones that this forum sends. Gmail's approach is to let everything in and then intelligently filter them into your spam box. Yahoo (and others) approach has been to completely deny emails coming from server blocks known to send large volumes of auto-generated emails. We have had problems with Yahoo in the past, along with Verizon and SBCGlobal. We are obviously at risk because of the number of large forum sites that we own and operate.
I will inform our network people that we are having another problem with Yahoo and they will investigate it. Hopefully, they will be able to make some progress on the issue.
From the tests that I've done, the mail queue is otherwise working properly.