public bool UseOpaqueSigning { get; set; }

Public Property UseOpaqueSigning As Boolean
	Get
	Set

Property Value

When signing only, using detached signatures is recommended (so-called cleartext signing). In this case, the signature will be added as a separate "smime.p7s" attachment. The message will still be readable even if the mail client of the recipient does not support S/MIME.

However, when you need to sign and encrypt (not just sign), you may consider using attached signatures (opaque signing, when the signature is embedded directly in the encoded message data as a single "smime.p7m" attachment). Due to encryption, the message will be unreadable anyway and this advantage of detached signatures is no longer relevant. For instance, MS Outlook by default uses clear-text signing when signing only and opague-signing when also encrypting.

Note

"Attached" and "detached" in terms of S/MIME signatures has completely different meaning than in e-mail and MIME. The result is an attachment in MIME terms anyway. In case of an attached signature the result is a single attachment (which internally has both the message body and signature encapsulated in a single encoded data block). In case of a detached signature the result is a the original message body and a separate attachment which represents a signature.

In opaque-signing mode, MailBee will produce this content-type: Content-Type: application/pkcs7-mime; smime-type="signed-data"; name="smime.p7m"

In cleartext-signing mode, MailBee will produce this content-type: Content-Type: multipart/signed; protocol="application/pkcs7-signature"

Reference