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 FixTechGuide support for Office 365 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 Outlook data file cannot be accessed 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 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.
• 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.

When the user is signed into their mobile app, webmail, or the credential loop in Microsoft 365 Windows Mail app, they are able to receive email perfectly fine with those. The issue is occurring only in the Outlook program installed on Windows. To update from Azure AD Sync to Microsoft Entra Connect, see the upgrade instructions.

Methods to fix Microsoft Outlook syncing error

If the size of your .ost file is close to the limit, you could try increasing the limit on your client, restart Outlook and see if there is any difference. If you're using an Outlook.com, Microsoft 365, or Exchange account, you won't have advanced mailbox settings unless the account was set up using advanced setup. The client has a computer off the domain at home that his work email is tied to and he has never had any of these issues in Cache mode with that device. I’ve unchecked download shared folders when setting up a new Outlook profile. Check with your email provider for instructions about how to create an app password for your email account. The Mail and Calendar apps for Windows 10 don't support two-factor authentication.

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.