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 Fix Outlook Not Opening After Windows Update programs or websites to be sure Outlook is the only problem.

Method 4: Recreating the Outlook Profile

If two-factor authentication is turned on for your account, you'll need to create an app password for that account. An app password is used instead of your normal account password for apps Troubleshoot Office 365 Sync and Login Issues that don't support two-factor authentication. Before you begin, make sure that your device has the latest operating system and app updates. Try the general troubleshooting solutions in Troubleshooting Mail and Calendar apps for Windows 10. Once you have completed the steps to fix Outlook sync errors, kindly check if the error has been fixed or not.

Check the connectivity to your email server

• This software also has a splitter option to split large-sized PST files into smaller ones, helping users prevent oversized PST file issues.
• You'll also receive a mail (to the alternate email and to your admin email) from Microsoft 365 that indicates your tenant has encountered directory synchronization errors.
• It is possible for a corrupted Outlook profile to impede synchronization.
• 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.
• Apart from this, we also discuss the Shoviv OST to PST Converter Tool, a professional way to repair, recover, and convert Outlook data files.
• Try the general troubleshooting solutions in Troubleshooting Mail and Calendar apps for Windows 10.
• I’m at wits end and Microsoft stopped helping me because they feel the problem is on our end.
• In some cases setting up a new computer replacement was the only option to fix these odd Outlook Sync issues.
• 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.

When the user is signed into their mobile app, webmail, or the Fix Outlook and Office 365 Errors 2025 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

I ran the PSTscan tool to check for anomalies on the OST file (which it found and repaired but the issue still occurs). However, with one particular client no matter what changes are made these sync issue still occur. We're sorry you're having problems with the Mail and Calendar apps for Windows 10. To fix the issue, please try each of the following solutions in order.

Microsoft Outlook Sync issues

Always make sure your profile and settings are set up correctly, your software is up to date, and your connection is steady. The causes of sync issues and local failures in Outlook are explained in this guide, along with practical troubleshooting and resolution techniques. You can extract and recover all of your mail items to a PST file using sophisticated OST File to PST Converter software if your OST file becomes unavailable or orphaned. Third-party firewalls or antivirus software might prevent you from syncing your email and calendar events. Check the software documentation to learn how to temporarily turn it off.