Problem
A Non-Delivery Report (NDR) is returned with the following error:
554 delivery error: There has been an error delivering your message to Crossware Mail Signature.
ErrorCode=2 (Cache Status set to relay)
Root Cause
This occurs when an external user (such as a contractor) is mistakenly added to an internal group that is referenced in the Crossware Microsoft 365 transport rule.
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The transport rule sends their email through the Crossware service.
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Crossware rejects the message because the sender’s domain is not configured within your Microsoft 365 tenant.
How to Fix
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Review the groups referenced in your Crossware transport rule.
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Remove the external user from any internal group used by the rule.
Once the external user is removed from the group, their messages will no longer be routed through Crossware and the error will be resolved.