Hi everyone.

We are using Microsoft Outlook 2010 to send encrypted and signed emails:

• We have a trusted authority in order to generate certificates
• We have configured Outlook in order to use those certificates and send them with signed emails.

We have two users, they are both registered as contacts after each other have sent signed emails. Thus, both have the public keys.

The first user can send encrypted emails. The second one can read them but he can not answer to an encrypted email. When he clicks on the Send button, he receives the following message :

"Microsoft Outlook had problems encrypting this message because the following recipients had missing or invalid certificates, or confliting or unsupported encryption capabilities:"

It then lists his correct email address and offers to send Unencrypted or Cancel.

We have noticed these different points :

• When we click on the button to reply to an encrypted email, in the field "To" it does not put the Display Name of the contact but his email address.
• When we decide to delete the email address in the "To" box and we choose the Display Name that Outlook proposes, we can send the encrypted reply message.
• When I reply to a regular (unencrypted) email, it puts the display name in the "To" box. When I decide to encrypt it before to send it and I click on the button "Send", I have the same problem. Besides, in the "To" box, it is not the Display Name anymore but only the email address.

Hi,

You may receive the error message if the email address of the contact or recipient is different from the email address that is specified in the recipient's certificate. A solution to prevent Outlook from displaying this warning message is listed below:

Important Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

• Click Start,  click Run, type regedit in the Open box, and then click OK.
• Locate the following registry key: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\14.0\Outlook\Security
• If a  Security registry  key does not exist, create a new key. To do this, follow these steps:
  1. Click the following registry key:  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\14.0\Outlook
  2. On the  Edit menu, point to   New, and then click Key.
  3. Type   Security, and then press ENTER.  
• Right-click the Security key, click New, and then click DWORD Value.
• Type SupressNameChecks, and then press ENTER.
• On the Edit menu, click Modify.
• Type 1, and then click OK.
• On the Registry menu, click Exit.

For more information, you can refer to this kb below:

https://support.microsoft.com/en-us/kb/276597

Regards,

Melon Chen
TechNet Community Su

Thank you for the answer.

I tried your solution but It didn't work.

Besides, the email address is exactly the same with the one in the recipient's certificate (we put it in the subject name and subject alternative name).