How to Fix Outlook 2021/2019/2016/2013 IMAP Sync Issues?

When you add or configure an IMAP-based email account in Outlook, it creates an OST file to store an offline synchronized copy of mail items, such as emails, contacts, attachments, notes, tasks, etc. on the local storage. This OST file is frequently synchronized with the mailbox server when Outlook is connected to the internet. Any changes made, when offline, such as drafting a new email or deleting messages, are stored in the OST file and synchronized with the mailbox server when the system connects to the internet.

With proper settings and configuration, synchronization between the Outlook client and IMAP mailbox server remains intact and this helps ensure uninterrupted email flow. But sometimes, you experience synchronization issues between Outlook and IMAP mailbox servers that can prevent you from sending or receiving new emails.

Due to slow or no synchronization between the Outlook client and mailbox server, you may experience problems, such as:

• Failure in sending or receiving new emails.
• Mismatch in number of emails between Outlook and webmail.
• Sync errors while manually synchronizing the mail items from OST to the mailbox server.

Thus, fixing the Outlook IMAP sync issues is critical. Let’s see how to resolve such issues. But before that, let’s understand the reasons behind the sync issues in Outlook.

Reasons for Outlook IMAP Sync Issues

Below are some reasons that may trigger sync issues in Outlook 2021, 2019, 2016, and 2013:

• Oversized or large OST file
• Faulty or incompatible add-ins
• Corrupt Outlook mail profile
• Hardware or software issues
• Lack of permissions
• Network issues
• Damaged or corrupt Outlook data file

Methods to Resolve IMAP Sync Issues in Outlook 2021, 2019, 2016, and 2013

Below we have discussed some methods to troubleshoot and fix Outlook 2021, 2019, 2016, or 2013 sync issues. Follow these methods in the given order.

Note: Security Updates KB2837618 and KB2837643 have caused problems, such as synchronization issues in Outlook IMAP account. Check your system for these security updates and uninstall them. The updates were released back in 2013.

Method 1: Check Network Connection

Synchronization requires an active network connection with the mailbox server. Unreliable and poor network connection or firewall settings can obstruct Outlook from synchronizing the mail items stored in the OST file to the mailbox server. Similarly, if the mailbox server is down, it can prevent Outlook from synchronizing the mail items.

To troubleshoot the issue, try reconnecting the network cable or WLAN. Then, check the internet connection and firewall settings. You may also contact your IT support to ensure that the network firewall isn’t blocking the mail server. Also, log in to your email account using a web browser to ensure your account is active and the server is available.

Method 2: Update Outlook

Updating Outlook and Windows may fix any incompatibility issues with the Outlook that could be the reason behind the synchronization issues. To check and update Outlook, follow these steps:

• Open Outlook.
• Navigate to File > Office Account > Update Options and choose Update Now.

• If a new update is available, download and install it. Complete the Outlook update wizard.
• To download and install Windows updates, follow these steps: Open Settings, go to WindowsUpdate and click Check for Updates.

• If available, install the updates and restart the system.

Method 3: Increase Server Timeout Setting

Sometimes, synchronization requires more time due to slow internet connection. However, longer synchronization may trigger timeout and lead to synchronization issues. To overcome this, you can increase the server timeout duration. The steps are as follows:

• In Outlook, go to File > Account Settings > Account Settings.
• Select the Outlook profile and click Change.
• Click More Settings and then click the Advanced tab.

• Here, you need to move the slider towards Long to increase the server timeout duration.
• Click OK and then restart Outlook.
• This setting may or may not be available in your Outlook based on the policies and settings of your organization. 

Method 4: Disable/Remove Faulty or Incompatible Add-Ins

Faulty or incompatible add-ins may conflict with Outlook and prevent it from working properly, leading to sync issues. By disabling and removing add-ins, you can resolve the sync issues. For this, you need to first run the Outlook in Safe Mode. To open Outlook in safe mode,

• Close MS Outlook.
• Press Windows + R, type outlook.exe /safe and press Enter.

In safe mode, Outlook does not load add-ins by default. If in safe mode your Outlook works properly and sync issues are resolved, you need to find and then remove the add-in causing the issue. For this,

• Go to File > Options > Add-ins and disable all add-ins.
• Then, launch Outlook normally.
• Start enabling add-ins one-by-one to spot the faulty one.
• Then, remove the faulty or incompatible add-in to fix this issue permanently.

Method 5: Repair Outlook Profile

Outlook profile contains all the settings of the account. If the profile is damaged or corrupted, it can lead to plethora of issues in Outlook, such as sync issues with IMAP account. However, you can repair the corrupt profile to fix the issue. To repair corrupt or damaged Outlook profile, follow these steps:

• In Outlook, navigate to File > Account Settings > Account Settings.
• Choose your email profile under the Email tab and click Repair.

• Follow the onscreen instructions and Outlook wizard to repair the profile.

• Click the Repair button again to proceed.
• This may take a while to complete. You may be required to re-enter the credentials, such as email and password.

After the repair is complete, restart Outlook. Then, check if Outlook is able to complete the mailbox synchronization with the IMAP mail server.

Method 6: Create a New Outlook Profile

By creating a new Outlook profile, you can replace your corrupt Outlook profile and fix the issues. The steps to create a new profile in Outlook 2013, 2016, and 2019 are as follows:

• Go to Control Panel and click on Mail.

• Click on the ‘Show Profiles’ button and click Add.

• Type your new profile name and click OK.

• Configure your IMAP email account and then click Next > Finish.

• Choose ‘Always use this profile’ in the Mail control panel and then select your new profile from the dropdown.

• Click ‘OK’ and restart Outlook.

Method 7: Change the Root Folder Path for IMAP Account

Sometimes, Outlook fails to detect the default root folder path. In such a case, you can manually set the root folder path for your IMAP account by following these steps:

• In Outlook, go to File.

• Click Account Settings > Account Settings and then double-click on your IMAP email account.

• Click on More Options and then click on the ‘Advanced’ tab.
• Root folder path should display ‘INBOX.’ If not, enter Inbox and click ‘Save.’ 

• Click OK and then restart Outlook.
• After restart, click the Send/Receive tab and click Update Folder. Then, wait for the synchronization to finish.

Method 8: Subscribe Folders

In the Outlook IMAP account, you can choose or subscribe mail folder that you wish to synchronize. This can fix Outlook sync issues you face with any particular email folder. The steps are as follows:

• Open Outlook, right-click on your IMAP email account in the left pane and choose IMAP Folders.
• Click ‘Query.’ This will display all folders in ‘All’ and ‘Subscribed’ tabs. Ensure folders in both tabs are matching and have mail folders you want to synchronize.
• Subscribe to any unsubscribed folder and click OK.

Method 9: Rebuild Outlook Data File (OST)

You can also face the Outlook IMAP sync issues, if there is a problem with the OST file. To fix this, you can rebuild the default IMAP OST file. The steps are as follows:

• In Outlook, go to File > Account Settings > Account Settings and click on the ‘Data File’ tab.
• Choose the IMAP email account and click ‘Open File Location.’ This will open the folder location where the default OST is stored.

• Close the Outlook app and back up the default OST file to a safe location. Then, delete the OST. 
• Restart Outlook. This will create a new OST file.

Outlook will start and synchronize the mail items. In case the OST rebuild fails, it’s probably due to the reasons, such as your profile is either removed, disabled, or deleted from the IMAP mailbox server. However, you can prevent data loss and extract all mail items from your inaccessible or orphaned OST file to Outlook importable PST format using an OST to PST converter software, such as Stellar Converter for OST. It also helps restore missing mail items in case the issue is resolved but you find missing mail items or folders in the mailbox.

Conclusion

Sync issues in Outlook are common and may occur for various reasons. We have discussed various methods to troubleshoot and fix the Outlook IMAP sync issues and resolve the synchronization errors. If the OST file is damaged or corrupted, recreate the OST file, after taking its backup.

After recreating the OST file, if you find missing items, you can convert the backup OST file to Outlook importable PST using an OST to PST converter tool, such as Stellar Converter for OST. Then, import the converted PST file into your new IMAP OST file via Outlook Import Export wizard and restore the missing mail items.

The tool also helps you extract and save mail items from an orphaned or inaccessible OST file to PST format. Additionally, you can also import the mail items from OST file directly into live Exchange or Microsoft 365 account in a few clicks.

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About The Author

Ravi Singh

Ravi Singh is a Senior Writer at Stellar®. He is an expert Tech Explainer, IoT enthusiast, and a passionate nerd with over 7 years of experience in technical writing. He writes about Microsoft Exchange, Microsoft 365, Email Migration, Linux, Windows, Mac, DIY Tech, and Smart Home. Ravi spends most of his weekends working with IoT (DIY Smart Home) devices and playing Overwatch. He is also a solo traveler who loves hiking and exploring new trails.