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 work offline mode stuck programs or websites to be sure Outlook is the only problem.

Method 4: Recreating the Outlook Profile

Another which is shown below, is a user opens a new message, or replies to one, and lets it sit for a while. When they go back to the message and press send they get an error that the message has been deleted. Ive repaired the OST and changed cache fix MFA prompts not working mode to only cache 1 year.

Check the connectivity to your email server

• This software allows users to process numerous OST files at once without any size limitations.
• If your password isn't the problem, you might have a certificate error.
• 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.
• Moreover, it maintains the folder hierarchy and metaproperties of the data when processing Outlook data files.
• This can happen for days at a time, and then disappear for a day or 2, only to appear again.

After performing these steps, Outlook’s all folders will be synced to the server. If this method doesn’t work for you, navigate to other solutions. There can be several reasons for the Outlook synchronization error. Before Troubleshoot Office 365 Sync and Login Issues we know the solutions, we will understand a few common causes of the Outlook sync problem.

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

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. This software allows users to process numerous OST files at once without any size limitations. Moreover, it maintains the folder hierarchy and metaproperties of the data when processing Outlook data files.