After upgrading from Thunderbird 38.3.0 to 38.5.1, my Outlook365 account did not function properly (IMAP). In 38.3.0 I saw all my child folders and could send and receive no problem. When I upgraded to 38.5.1 only the Inbox was fully functional and the Sent folder displayed sent mail but I could not actually save any outgoing emails. The "could not save email" error message would pop up. I checked my Outlook365 server functionality using the Outlook client, which works fine, all folders displayed and all functions worked.. No outlook365 server updates or upgrades were made since June 2015. The only thing that changed was that I upgraded Thunderbird. I have reverted Thunderbird back to 38.3.0 and everything works fine. I took myself off automatic upgrades for Thunderbird. Mac, Yosemite. Is this an isolated problem?