Library /sys$common/syshlp/mailhelp.hlb DIRECTORY, Qualifiers, /TO_SUBSTRING  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /TO_SUBSTRING=text

    Selects messages containing the specified text in the To: field
    of the message, where the specified text is usually a node name
    or user name. The /TO_SUBSTRING qualifier will not search the
    personal name field.