HI, I believe there is some kind of issue with T-bird and Office365. I have a long existing account, hosted by godaddy. They forced me to move to Office365. Actually I have multiple accounts with multiple domains at godaddy in this situation. Recently one of the accounts quit working. It would pop up with a demand that I enter the password. Password entries all failed. I was able to continue accessing the email via Office365 web interface using my normal password. I tried talking to godaddy support which was a waste of time. I cross checked all of my settings with other email accounts to make sure this one wasn't set up strangely. It was not, and changes didn't help. The breakthrough was to mangle the existing account settings to give myself a faulty email address (I could have just deleted the account in T-Bird), then go through the new account auto setup. Using the same password as always, that worked fine. Now I am using it again just like I was. Enough has happened that my memory is not exact, but I believe that there was a "choose a new password" dialog that I had to brush off when I first went to web interface after the first failing of T-bird. So my suspicion is that there is some kind of old-password dialog going on with Office365 that T-bird is not handling well. I did not have to change my password, I'm still using the same one. So maybe it was my imagination. But still have that niggle in my mind that it was a password age issue. I did the usual google searching in my effort to find relief and it seems to me this problem between T-bird and Office365 is a regular recurring issue. It stays around for awhile and then evaporates (or the user gives up). I believe there is a real problem under there somewhere.