/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.

    The /USER qualifier has no effect on interactive PMDF MAIL
    sessions.