Due to the IMAP issues affecting Outlook 2013 and Office 365, users fail to. Option' option and look for the 'Root folder path' option, and then enter Inbox. Jan 19, 2016 - Outlook is constantly 'synchronizing folders. Tasks can accumulate so that Outlook is basically stuck in an endless synchronization process.

1. Outlook 2016 Stuck On Synchronizing Inbox
2. Outlook Stuck On Synchronizing Inbox Yahoo
3. Outlook Keeps Saying Synchronizing Inbox

Hello all,
As a precursor to this question, I normally deal with POP3 accounts so I am not sure what to do with this.
I have a client that has Outlook 2016 and is using an IMAP account through Network Solutions.
They do not have an Exchange server on site.
The issue is with synchronization. He has over 30,000 emails in his Inbox and over 19,000 in his Sent folder. I have suggested that he clean these up. He keeps getting synchronization issues where it just hangs. If we end Outlook then wait 5 minutes and start it up again we still get synchronization hanging. I have done a compaction and repair on his ost file. I have had Network Solutions do a resynchronization on his email account on their end three times in the past two weeks.
Nothing seems to be helping.
I have tried everything that I can find on the internet.
Whenever I suggest that he cleans it up, he comes back that his boss (who has an identical machine) has over 40,000 emails in her Inbox and over 30,000 emails in her sent folder and she never gets synchronization issues. And yes she is using Outlook 2016 with an IMAP account.
What can I do to fix this?
Should he go to Thunderbird?

Outlook 2016 Stuck On Synchronizing Inbox

Go to a PST account?

Outlook Stuck On Synchronizing Inbox Yahoo

I know he should delete emails but short of doing that what can be done?

Outlook Keeps Saying Synchronizing Inbox

Thanks,
Kelly W.