@Adam,

Mail.dll recognizes encrypted emails by content-type headers: application/pkcs7-mime or application/x-pkcs7-mime with smime-type set to enveloped-data or enveloped data found inside the actual asn.1 content. IsEncrypted does not actually check for content type as email parsing occurs much earlier.

Please also note that Mail.dll email component decrypts email messages automatically. For such decrypted messages IsEncrypted will be set to true (NeedsDecryption is false) although decrypted message does not contain application/pkcs7-mime content type any longer.

email.HasContentType method is most likely an extension method and was not developed by us.

Today I’m trying to ascertain what set of things the .IsEncrypted property takes into account. Specifically, does it contain a check for the content type call email.HasContentType(“application/pkcs7-mime”, “smime-type”, “enveloped-data”) ?

@Adam,

Now I get it. Your solution is correct. IMail.GetEnvelopedCms() is the way to go. I think that it’s also possible for the certificate itself to enforce some of those policies.

@Adam,

You need to be more specific than “it seems to chew on whatever I give it”.
What are you trying to do? Send encrypted email or decrypt the one you have received? Are you getting any exception? Error? From Mail.dll or from your email program?
Please read this article, if you need to specify SMIME encryption algorithm explicitly.