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For the past month and a half or so Outlook 2016 will continually prompt for username and password to a point where I have to close it and re open it. It also will not sync unless I close and reopen it. This is getting really annoying. First level support was all but useless. I'm a network and email tech and have done pretty much everything on my end. including:
1. Deleting and recreating my profile, my .ost file, and any other file involved.
2. Changed my password about 5 times, this will work for about an hour then it starts doing the same thing though it still doesn't sync.
3. Verified all my settings and tested.
Basically first level support said they don't support 3rd party products like Outlook and to use the webmail. This is not acceptable. I read a similar post a couple of weeks ago where moving their account to a different email server solved the trick.
Please try deleting your cookies and cache first, then restart your computer. Also have you changed your password, but did not change it in your advanced settings?