The envelope From: address for a message to be sent should be specified with the PMDF_USER item code. With this item code, only a user name may be specified; PMDF_send will automatically append the official local host name to the name so as to produce a valid address.
The PMDF_ENV_FROM item may be used to specify an envelope From: address which is not a local address. This is usually not necessary: applications which enqueue non-local mail should probably be using the API routines rather than callable SEND.
If neither PMDF_USER or PMDF_ENV_FROM are specified, then the user name
associated with the current process will be used for the envelope From:
address. When PMDF_USER is used, the From: header line address will be
derived from the envelope From: address; when PMDF_ENV_FROM is used,
the From: header line will be derived from the user name of the current
process.² Only privileged users may specify with PMDF_USER a user
name different than that of the current process's. On OpenVMS systems,
WORLD privilege as a default privilege is required. On UNIX systems,
the process must have the same (real) UID as either the
root or pmdf account. On NT systems,
PMDF_send can only be used by privileged accounts such as Administrator.