How to fix error 0x8004210a in MS Outlook Manually?

Try the following manual fixes to resolve the 0x8004210a error. Proceed to the next fix only if the previous one fails. After complete the steps mentioned in each fix, send yourself a test mail to check if it worked.

1. Configure your Antivirus program and Windows firewall and enable unrestricted access to Outlook (outlook.exe)
2. Delete suspicious emails from your mailbox as they may block your receiving error message in Outlook. Also, clean up pending messages stuck in the Outbox
3. Launch Outlook in safe mode by typing outlook.exe /safe in the Windows Run dialog to see if send-receive works. If it does the culprit might be a faulty Outlook add-in
4. Increase server timeout duration as follows:
   1. From the Outlook ‘File’ menu option open Account Settings
   2. Select the affected email account and click on ‘Change’
   3. Click on ‘More Settings’
   4. In the ‘Internet Email Settings’ pop-up window, switch to the ‘Advanced’ tab and increase the server timeout time according to the requirement
   5. Click on ‘OK’
5. Repair your Outlook installation by going to Control Panel, selecting MS Office and clicking on ‘Repair’
6. Create a new Outlook profile and try to send-receive email using it. Follow the below-mentioned steps:
   1. From Control Panel -> Mail -> Show Profiles select your current Outlook profile and view its ‘Properties’ to know its exact location
   2. Then again go to Control Panel -> Mail -> Show Profiles and click on ‘Add’ to create a new Outlook profile
   3. Give it proper details and click on ‘Finish’ to complete setup for the new profile
   4. Thereafter from Control Panel -> Mail -> Show Profiles select the profile you just created and select the ‘Always use this profile’ setting to set this profile as the default
7. If none of the above methods works, then there could be the reason that you PST File is corrupt, try repairing your existing Outlook PST file using Microsoft’s default Inbox Repair utility ScanPST.exe.