Microsoft Outlook Cannot Sign or Encrypt This Message (Fixed)

I encountered "Invalid Certificate: Microsoft Outlook cannot sign or encrypt this message because there is no..." error? This article will discuss the causes of this error and the corresponding solutions.

Why does an invalid certificate appear?

Why can't Outlook send encrypted emails? There are several common reasons why Outlook encryption problems can be caused:

• Hostname entry error: Incorrect hostname settings or entry errors may cause email sending to fail. This is one of the easiest reasons for this error.
• Date and Time Error: If the computer's date and time settings are incorrect, it may cause problems with the Outlook security certificate, resulting in a "Microsoft Outlook cannot sign or encrypt this message..." error.
• SSL Port Blocked: Blocked SSL Port may also cause certificate errors.
• Problem Add-in: Third-party plug-ins can cause many problems, one of which is the Outlook encryption problem.

After understanding these reasons, you can try the following workaround.

How to fix Microsoft Outlook's inability to sign or encrypt this message?

How to fix the error that Outlook cannot send encrypted emails? Based on the basic reasons mentioned above, we will show you some simple and easy solutions.

1. Verify the domain name and port

Sometimes, wrong domain names and ports can cause encryption problems, especially if there are subdomains like. Please follow these steps to verify that the domain name or port is correct:

Step 1: Access the email configuration settings on your computer and find the email settings. Then look for the SSL/TLS settings of the device.

Step 2: Check the domain names of the receiving and sending servers to make sure that the names ( IMAP , POP3 , and SMTP ) are correct.

Step 3: Open Outlook and click the File tab.

Step 4: Under Account Information , click Account Settings , and then select Account Settings from the following menu.

Step 5: In the pop-up window, click the Change tab and select the More Settings button.

Step 6: Select the Advanced tab in the new window. You can then check if the configured port is wrong. Change it according to your situation and click OK to save the change.

2. Delete Outlook add-in

Outlook encryption issues may be caused by third-party plug-ins installed on Office. Deleting these add-ins might be a way to fix this error.

Step 1: Start Outlook, select the File tab, and then click the Options tab from the left pane.

Step 2: Locate the Add -in tab from the menu on the left and look for the Admin section at the bottom of the window. Click Go to next to COM Add-in to open a new window.

Step 3: Uncheck all third-party add-ins and click the Delete option. When finished, click OK to save the changes.

Also read: How to install and manage add-ins in Microsoft Outlook

3. Replace the sending server number

To fix Outlook's inability to sign or encrypt this message, you should try to change the sender SMTP server port number.

Step 1: Open the Outlook desktop application and select the Files tab.

Step 2: Select the Account Settings button and click Account Settings from the drop-down menu.

Step 3: Select your email account and select the Change option in the Email section.

Step 4: Click More Settings in the new window. Then select the Advanced tab and check the server port number. If necessary, replace the sending server (SMTP) number with another port number. Click OK to save all settings.

Conclusion

This article discusses several reasons why Microsoft Outlook cannot sign or encrypt this message and describes the corresponding solutions. Hopefully you can find an effective solution.

Additionally, if you are concerned that files stored on your computer may be at risk of loss, you can use backup software to back up Outlook email or data to another location, such as an external hard drive. We recommend that you use MiniTool ShadowMaker, a professional backup software.

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