I use a desktop running Outlook 2016 (32) on Windows 10 (64) Pro. I have 3 accounts attached: 2 IMAP accounts and 1 POP3. I I leave all the messages in my IMAP accounts on the server until the end of the year. Each new year, I offload the previous year's IMAP mail as well as start a fresh POP3 data file, so that I have "minimal" emails on the server. I also have an Android phone that attaches to these 3 accounts. Outlook 2016 hangs pretty much every day on the synchronizing step. It appears to be only in the IMAP accounts, but it can hang on any of the folders within the IMAP account. I am ASSUMING that Outlook on my PC is trying to sync with the server, which is in turn trying to coordinate the sync between the PC and the phone. IDK. I ran SCANPOST on all 3 files, which did correct some errors, but that did not solve the problem. Any suggestions? I've read a ton of posts on sync problems, but none seem to be related to sync-ing when IMAP accounts are involved. When it hangs, I cannot do anything except either wait (currently 3 hours) or end the Outlook task. The next time I go in it just starts up the sync again. Thanks for the help.
I just MAY have solved it. Over time, Outlook 2016 (32) desktop accumulated deleted draft messages. In other words, there were an increasing number messages showing in my Drafts folder that had a cross-out through them. I couldn't delete them from within Outlook. BUT, when I went into my email account through the server (i.e., webmail) I went into that Draft folder, and all the messages were gone. So then I went back into Outlook and those pesky deleted drafts disappeared. I went back into webmail, and just opened each folder in my email account, just to be sure. When I then went back to Outlook, everything seemed to be cleaned up and I have not had Outlook hang since!