Library /sys$common/syshlp/nclhelp.hlb set, session_control, application, incoming_proxy  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: True          Value: True or false

    Specifies whether to honor incoming proxy requests. If this
    attribute is set to false, requests to invoke proxies on
    incoming requests are ignored. The setting of this characteristic
    overrides the setting of the session control incoming proxy
    characteristic for the specified application.

    Example:

    set session control application mail incoming proxy false