Fixing Outlook Security Certificate Error

Question

How can the issue be resolved when the following error continuously appears on an Outlook email account: “The server you are connected to is using a security certificate that cannot be verified. The target principal name is incorrect.”?

Answer 1

Hi TXIS

Welcome to Microsoft Q&A Forum!

First and foremost, I understand how frustrating this can be, especially when it disrupts your daily workflow and email communications, and we're truly sorry for that. Our support team is committed to helping you resolve this issue as quickly and effectively as possible. 

Based on your description (the error "The target principal name is incorrect" when connecting to the email server), this is a common issue that may stem from account configuration or temporary cache problems. Below, I've outlined some basic steps you can try to fix it. I'll guide you through each one in detail for easy follow-up. If you're not comfortable with technical steps, please proceed one at a time and note the results. 

Match Certificate Name (Initial Check for Certificate Mismatch) 

To fix the error that the server you are connected to is using a security certificate that cannot be verified, you can check whether the certificate name matches the mail server. 

First, could you please confirm if the error message you see looks similar to this?  

If it matches, here's the tutorial: 

1. When you receive this Outlook error message, click View Certificate in the warning dialog. 
2. In the certificate details window, check the "Issued to" name and make sure it is the same as the name of your mail server (you can get the correct server name from your email provider or IT department, e.g., something like "mail.example.com"). 
3. If it does not match, note the discrepancy and contact your IT support to correct it (e.g., update the server configuration or certificate). Then, try connecting again. 
4. After that, re-open Outlook and check whether the error is resolved. 

Restart Outlook and Your Computer  

1. Completely close Outlook (check Task Manager to ensure it's not running in the background). 
2. Restart your computer. 
3. Reopen Outlook and check if the error persists. Sometimes, a simple restart resolves temporary issues. 

Remove and Re-Add the Email Account 

1. Open Outlook. 
2. Go to File > Account Settings > Account Settings. 
3. Select the email account experiencing the error (usually an Exchange or Microsoft 365 account). 
4. Click Remove to delete the account (Note: Your local emails and data will remain if you're using an OST file, but remember to back up as mentioned above to be safe). 
5. Then, click New to re-add the account: Enter your email and password; Outlook should auto-configure it (if not, select manual setup and enter server details from your email provider). 
6. Test again to see if the error is resolved. 

Clear the Autodiscover Cache  

1. Completely close Outlook. 
2. Press Windows + R to open the Run dialog. 
3. Type %localappdata%\Microsoft\Outlook and press Enter (this opens the Outlook data storage folder). 
4. Locate and delete the RoamCache folder (if it's not visible, enable "Show hidden files" in File Explorer). 
5. Reopen Outlook and try connecting again. This clears temporary cache, allowing Outlook to rediscover the correct server. 

If the Error Persists: Delete the Outlook Profile and Rebuild the Account 

1. If the previous steps don't help, you may need to delete the Outlook profile (user configuration) and rebuild it from scratch. 
2. Open Control Panel (search for it in Windows Search). 
3. Find and open Mail (or "Mail (Microsoft Outlook)"). 
4. Click Show Profiles, select the profile in use (usually "Outlook"), and click Remove. 
5. Then, click Add to create a new profile, and re-add your email account as in Step 3. 

Important Note Before Starting: To avoid any potential data loss, please ensure that you back up your important Outlook data safely beforehand. Store the backup in a secure location, such as an external drive or cloud storage.

Thank you for your patience and understanding. I realize the initial response may not fully resolve the issue or capture the situation accurately. I’d greatly appreciate any updates or additional suggestions you can share. 

If you encounter difficulties with any step or the error continues (e.g., a more specific error message or screenshot), please let me know more details! I'll provide further advanced steps based on that information. We're here to ensure you can use Outlook smoothly again. 

Thank you for reaching out and trusting us. Have a great day! 

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