I get the following error when encrypting a mail with MailMessage.Encrypt, but couldn't find anything in the source or online regarding this error message:
"No recipient has a certificate with correct key usage for encryption."
The certificate is valid and has the following purposes listed (the first would read "Protects E-Mail messages" in English):
"Schützt E-Mail-Nachrichten
1.3.6.1.4.1.22177.300.1.1.4"
Any idea what's causing this and how I can circumvent it?