Relevant Products: Exclaimer Cloud - Signatures for Office 365
You are using Exclaimer Cloud. When a signed or encrypted message is processed, no signature will be appended.
This is expected behaviour when using the server-side signature rules. It ensures that security on the message is preserved and un-tampered with when the message is delivered to the intended recipient.
It is possible to apply a signature to encrypted messages using the client-side signature rules. This is because the signature is present when the message composed, so the message is not processed by our servers.