I've a mail message type task that sends a message to a user sap. I've concatenated the variable that holds the user following: 'US' + 'SAP USER'.
And I configurated as Express message too. But this message don't get SBWP inbox and don't pop up on user screen.
ps.: after this message, I've a mail message type, and this message is ok. It gets the user's external mail inbox.