VMS Help SET, HOST, /DTE, Qualifiers, /FLOW_CONTROL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /FLOW_CONTROL (default)
       /NOFLOW_CONTROL

    Determines whether XON/XOFF flow control is enabled. By default,
    flow control is enabled.

    XON/XOFF flow control is a means of preventing data-overrun
    errors. Incoming data is stored in receive buffers; when these
    buffers are full, a signal is sent to the remote system to stop
    transmission. Once there is sufficient space in the receive
    buffers, another message is sent to restart transmission.

    You should disable XON/XOFF flow control when the remote system
    has no XON/XOFF flow control.