Use of the -G command-line switch indicates to sendmail that the message being submitted from the command line is for relaying, and is not an initial submission. This switch is primarily intended for use by the rmail(8) program, a part of the UUCP suite of programs. Mail received by UUCP is mail that did not originate at the local site. It is intended to be relayed outward to other sites, or to be delivered locally. Because mail received by UUCP is not the initial (therefore, local) submission of a message, sendmail needs to be more strict about what it will accept.

A message received with the -G switch specified will be rejected if the address is not fully qualified. The -G command-line switch also tells sendmail to perform no canonicalization on the address. Note that future releases of sendmail might reject improperly formed messages when this switch is specified.