Resolve sync issues in Mail and Calendar apps in Windows 10

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The other solution to fix Outlook sync issues is recreating Microsoft Outlook profile.



solve Office 365 mailbox sync delays

The diagnostic will guide online Outlook email repair utility you to resolve various error conditions that can cause mailboxes to not be created. The most common cause of an out-of-date account is an incorrect password. In the notification bar at the top of the app, select Fix account.

solve Office 365 mailbox sync delays

Turn off Windows Defender Security Center



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. Outlook Not Sending or Receiving Email I’ve unchecked download shared folders when setting up a new Outlook profile. 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. Select the button below to launch a diagnostic in the Microsoft 365 admin center.

solve Office 365 mailbox sync delays

Check if two-factor authentication is turned on for your account



solve Office 365 mailbox sync delays

If your password is incorrect, you'll see a message asking you to update your password. 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. Once you have completed the steps to fix Outlook sync errors, kindly check if the error has been fixed or not. There can be several reasons for the Outlook synchronization error. Before we know the solutions, we will understand a few common causes of the Outlook sync problem.

Check Antivirus and Firewall Settings



  • This tool also helps users fix Outlook syncing issues by repairing OST or PST files and syncing the data smoothly.
  • 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.
  • Test other programs or websites to be sure Outlook is the only problem.
  • However, with one particular client no matter what changes are made these sync issue still occur.
  • This solution will be beneficial for users who are facing Outlook syncing issues because of corrupted PST or OST files.
  • I have a couple of Users and a Shared Mailbox that were migrated and both Users are experiencing issues with the Shared Mailbox updating on a regular basis.


If you can sync your email when the firewall is turned off, you'll need to allow the work offline mode stuck 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.

Free Methods to Remove Duplicate Items in Outlook 2016



If you're using an Exchange account that requires advanced settings, you'll need to remove the account and add it again using advanced settings. To add the account using advanced settings, see Add an account using advanced setup. Knowing the reasons behind the online Outlook email repair utility sync issues will help us to fix this problem and prevent issues in communication and workflow. If you still can't sync your email after removing your account and adding it again, you might need to add the account using advanced setup. If I check the sync log I see a lot of sync errors for Inbox, sent items and a few other folders.
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