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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 how to fix Outlook not opening today 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 diagnose Office activation conflicts is not from a trusted certifying authority."

Check the connectivity to your email server

We have resources to help you identify potential issues and fix them.The Support and Recovery Assistant, a tool provided by Microsoft, can identify and resolve common Outlook problems.Below are the steps I’ve taken to try to resolve this issue.Firewalls and antivirus software might prevent you from syncing your email and calendar events.If so, you'll see a message that says, "There is a problem with the server's security certificate. The security certificate is not from a trusted certifying authority."This solution will be beneficial for users who are facing Outlook syncing issues because of corrupted PST or OST files.

However, his OST file is not anywhere near that size it’s about 5GB. I was wondering if anyone had some insight into an issue I am having with a client. Additionally, you might want to make a new profile and make it the default to see if it fixes the problem. Create your account modern authentication troubleshooting and connect with a world of communities.

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

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.