/USER=username

    Specify the local username to use in the message sender's
    address; (this will be the From: address if no other From:
    address is given and the Sender: address otherwise). You must
    either have WORLD privilege or hold the PMDF_WORLD or PMDF_WORLD_
    username rightslist identifier in order to use this qualifier
    and specify a username other than your own. The special case of a
    blank string will not insert any Sender: information.