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Problems in Microsoft Outlook - missing or invalid certificates

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Microsoft Outlook had problems encrypting this message because the following recipients had missing or invalid certificates or conflicting or unsupported encryption features.


Secure bidirectional communication is achieved in that both sides have certificates and both parties give everyone their public key. In this case, anyone can send an encrypted (secret) message to one of these two people from anywhere. These two people have the same ability and can now send each other's encrypted messages to each other using the other person's public key.


This also works with digital signatures. So that a person who receives a digitally signed message can read it, your public key is sent with your message. To ensure that the public key supplied with the message is actually related to the actual sender and is not just invented, Sectigo inserts its own signature in your certificate to secure your claim.


In order for Outlook to send an encrypted email to another person, a valid certificate must be assigned to the contact who is the intended recipient of the encrypted message. A signed email is the best way to distribute this certificate to those who want to send you encrypted messages. To exchange encrypted messages, the sender and recipient must have a signature and encryption certificate.

To ensure that a contact has been assigned a certificate in Outlook, do the following:

Six steps to check the existence of the certificate /

  • Open the signed email message that you received from the recipient.
  • Klicken Sie in der Betreffzeile dieser signierten E-Mail mit der rechten Maustaste und wählen Sie «Zu Kontakten hinzufügen».
  • If the sender is not in your address book, a contact window is displayed. Enter the information you want to include, e.g. B. First and last name and other details.
  • Once added, click Save and Close. This will automatically add the sender's digital ID to your contact address book.
  • If the sender already exists in your contact book, a dialog box with double contacts is displayed. Click OK to update the new information.

You can now send an encrypted email to your recipient.

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