Arthur Pemberton wrote:
What is the difference between "S/MIME" and "S/MIME opaque" ?
Although I haven't used opaque signing, I've seen it explained thusly:“Opaque” signed messages are encoded such that the recipient requires an S/MIME-enabled e-mail client to automatically read the message.
I take it to mean that an opaque message is encoded (not encrypted) so that it's not plain text, but can be decoded by anyone with an SMIME-enabled client.