I'm running Tbird 45.1.0 on a MBPro running 10.9.5. I can receive emails without problem for any of the accounts I have set up. The problem lies in trying to send email. Recently, Tbird will start to send, connect to servers but the when the status is 'Delivering mail', it will stop at some percentage (e.g. 88% or 54% or whatever) and stay there with no progress until it times out... I'm confident that the server settings are correct and that I'm not blocked by either my ISP or my host (my host confirmed settings using Teamviewer so I'm good there). I have been running close to hard drive capacity and I'm concerned that something had become corrupt. I also have folders with quite a few emails so I'm wondering if I've hit a capacity issue (I'm going to be deleting old emails as part of this just in case) Is there a way to "un-corrupt" or rebuild a prefs file to help Thunderbird get it's groove back?