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.
Alternatively, if using server-side signatures, the signature would need to be applied before the message is encrypted. If you use a transport rule to encrypt messages, provided the Exclaimer transport rule has a higher priority and is processed before the encryption transport rule, the message will have a signature applied.