Using IMF with S/MIME-Encrypted Email

What does Microsoft Exchange Intelligent Message Filter (IMF) do with email that's been signed or encrypted using the Secure Mime (S/MIME) standard?

By design, IMF ignores such email. The tool can't read S/MIME-encrypted messages; furthermore, the fact that the message was encrypted to a particular recipient is considered reasonable evidence that the message is legitimate. For the same reason, the tool doesn't scan signed messages.

—Paul Robichaux

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