Why Sync has Stopped Working in Outlook Online Microsoft 365? [7 Method]

Did synchronization stop working in Outlook Online? This article is exactly what you are looking for to check why sync has stopped working in Microsoft Outlook 365.

I am using Microsoft Outlook 365 for a long time, sometimes it fails to synchronize. I searched for many reasons and then found the proper solution.

We will also talk about the symptoms and troubleshooting techniques as well. Here we go to see the below steps and how it is working.

Why is Outlook not syncing?
Fix the email sync issue from Outlook web
Symptoms of synchronization problems
Resolve sync issues in Outlook Mail
Repair the Outlook sync issue using the run option
Configuring Outlook settings
Turn off third-party security software
Remove your Outlook account and add it again

Table of Contents

Why is Outlook Online not Syncing?

Our Microsoft Outlook 365 application will not be syncing due to the forthcoming reasons. However, by below approaches, we were able to fix the issue effortlessly.

The first and foremost reason behind not syncing Outlook is because of faulty server connections.
Due to OST file corruption problems, offline changes (OST changes) do not sync with connected changes.
Configuration of IMAP or POP settings will be faulty.
Microsoft Outlook 365 application will be corrupted.

So, if the above method doesn’t work out then move ahead with the below methods to see what was the exact issue.

Fix the Email Sync Issue from Outlook Online Web

Microsoft Outlook 365 shows the mobile device that we have connected. If we no longer use a device that will not sync properly, we can delete it from the list. By doing that there will be an unlink between mobile and PC. Removing this partnership between mobile and PC by following the steps below often fixes sync issues.

Sign in to the Microsoft Outlook Online 365 application.
Go to the settings icon or gear icon and scroll down to see View all settings, hit on that to move to the subsequent proceedings.

Fix sync issue in Outlook Online browser

On the next settings page, click General and simultaneously click Mobile devices. If you have linked with the Outlook application just delete it with this current PC. Since I have not synced any mobile devices so unable to share screenshots.

Unsync mobile device to check Sync in Outlook Online

If you want to remove your mobile device from the Microsoft Outlook application, then we can leave it till this step.
Go to your mobile device and shut it down for a while.
Restart your mobile device after some time, and then sync your mailbox again.

Symptoms of Synchronization Problems in Outlook Online

When synchronization issues occur in Microsoft Outlook or in Microsoft Outlook Web App, we may experience the following symptoms.

We can see the mismatches between the emails that we receive in Microsoft Outlook 365 application.
We may have an issue with Outlook but the issue does not visible when the cached mode is disabled.
In sporadic cases, we will receive an error message while we try to synchronize with the offline folder. We can see the below error message.

Cannot start Microsoft Outlook or cannot open the Outlook window.

We will feel some missing items such as emails, appointments, contacts, and documents from our mailbox.

Resolve Sync Issues in Outlook Mail

Resolving sync issues in Microsoft Outlook Online is not a big deal. Since we should make sure to know about troubleshooting synchronizing issues to avoid big problems.

Fix Outlook Issue in Outlook Desktop Application

When Outlook Syncing is not working need to fix it immediately with our Microsoft Outlook account. Check the below steps to know the procedure.

Open Microsoft Outlook in the desktop application and move to the File tab.
Below the Account information, click the Account settings option to check why sync is not happening.
The Account settings page will open, select the required account (if you handling multiple accounts) which is failing in syncing then click the Repair button.
Now, the Repair Account page will appear. In this check the necessary fields and click Next.
Outlook will start the repairing process to synchronize with the emails.

Change the Account to Check Outlook Online is Syncing

Once the above process is completed, check the below steps as well to verify the email even if it is still not syncing.

Move ahead to the file in the Microsoft Outlook desktop application, click on Change Account settings, check Test Account settings then simultaneously click Next.
Now, Microsoft Outlook will automatically test the account settings, and provide a message when everything is fine without issue. Once you get this message, click Close. Finally, click on the Finish button.

That’s it. Restart Microsoft Outlook and see if the issue has been solved. If required, we can also synchronize manually the first time using Send / Receive button.

Repair Outlook Online Sync Issue Using the Run Option

Try this below method as well to check if the sync is working properly or not.

Go to the Run tab in Windows.
Type ncpa.cpl.

Select your connection and Right-click on it.

Go to Properties and make sure that the Internet Protocol (TCP/IP) check box is selected.

Configuring Microsoft Outlook Online Settings

Let’s check how Microsoft Outlook changes are made to sync in the below steps.

Go to Start and select Settings -> Privacy -> Email.
Make sure that Let apps access and send email is set to On.
Select Calendar from the Outlook application.

Ensure that Let apps access my calendar is set to On.

Turn off Third-Party Security Software to Sync in Outlook Online

Third-party security software or antivirus might stop syncing our Microsoft Outlook email. Though we do not need to permanently turn off the security software, temporarily turning off the software will check if it is preventing us from syncing. Check the software documentation as well to temporarily turn off the software.

Important Note: If we disable your antivirus software, should not open any email attachments or click any links in messages from people we don’t know.

Remove Your Outlook Online Account and Add it Again

In some instances, we can resolve sync issues by removing our account from the Mail and adding it again.

Go to the start menu and open Mail.
At the bottom of the navigation select settings opinion or click the gear icon.
On this page, select Manage Accounts.
Select the required account you want to remove and Delete the account from this device.
Add the account again after sometime to check synchronization is occurring with the Microsoft Outlook 365 application.

End Point

I have given all the necessary information regarding why synchronization does not happen in Outlook Online. Hope this article helps you to check out the exact reason for not synchronizing in Outlook Online.