If you can sync your email when the firewall is turned off, you'll need to allow the Mail and Calendar apps through the firewall. Windows Defender Security Center is free security software that's included with Windows 10. If you haven't installed alternative security software, you should temporarily turn off Windows Defender Security Center. Test other Outlook OST vs PST repair programs or websites to be sure Outlook is the only problem.

Method 4: Recreating the Outlook Profile

However once I joined this computer back to the domain and let it sit for a few days it was also working fine. Once the client started using Outlook again after some time has passed the issue had come back. I’ve tried to set cache mode from 1 year all the way down to a few days. If your password isn't the problem, you might have a certificate error. If so, you'll see a message that says, "There is a problem with the server's security certificate. The security certificate Office 365 Sync Errors Fix is not from a trusted certifying authority."

Check the connectivity to your email server

• Before finding solutions, we suggest that users check their internet connection.
• This software allows users to process numerous OST files at once without any size limitations.
• If users are facing syncing issues in Outlook due to corrupt Outlook data files, they must choose a professional tool, like Shoviv OST to PST Converter Tool.
• Two-factor authentication helps protect your account by making it more difficult for someone else to sign in.
• After performing these steps, Outlook’s all folders will be synced to the server.
• The Mail and Calendar apps for Windows 10 don't support two-factor authentication.
• This can happen for days at a time, and then disappear for a day or 2, only to appear again.

You'll also receive a mail (to the alternate email and to your admin email) from Microsoft Repair Outlook Profile Online 365 that indicates your tenant has encountered directory synchronization errors. For details see Identify directory synchronization errors in Microsoft 365. I still have it turned on on my laptop and it has not shown any issues yet.

Methods to fix Microsoft Outlook syncing error

If the connection is poor, consider restarting your modem/router or moving to a more reliable network. After these instructions, ensure the sync settings are correct and check everything is working well. I’m at wits end and Microsoft stopped helping me because they feel the problem is on our end. However, I cannot find any reason why his account would do this only on our domain nothing is blocking our connection to Office 365. Here is the strange part I tried to remove the computer from the domain and have Outlook run from a local account for a few days.

Microsoft Outlook Sync issues

I’ve tried the Microsoft office uninstall tool provided by Microsoft (which deletes more items then just control panel uninstall). Below are the steps I’ve taken to try to resolve this issue. Two-factor authentication helps protect your account by making it more difficult for someone else to sign in. It verifies your identity using your password and a contact method (also known as security info). Outlook will show as connected to Exchange but is not receiving any new email. This can happen for days at a time, and then disappear for a day or 2, only to appear again.