However it indicates new, unread messages are available but obviously doesn't display them. If I try to send an email I get the following error message "Sending of message failed.". I use Thunderbird on a couple of different Windows systems and I am not having this problem. The last emails that were synced were from about a week ago which is about the time I did the Mac system update. I'm on a MAC OS X 10.9.5 using TBird 31.1.2 and I am trying to sync an account that is a Microsoft Exchange and I have ExQuilla 31.0.1135 add-on installed. If anyone has an idea what is going on here I would love the help in resolving this. Thank you.