As part of the RFC2554 authentication
scheme, a client can ask if a user other than the envelope sender is
allowed to authenticate on behalf of the envelope sender. This is
done by adding an AUTH= parameter to the MAIL FROM: keyword:
MAIL FROM: <user@host.domain> AUTH=address
This ${auth_author} macro is assigned the
address that followed the MAIL FROM: AUTH=
extension.
The ${auth_author} macro is useful for adding your
own rules to the Local_trust_auth rule set. Note
that a $& prefix is necessary when you
reference this macro in rules (that is, use
$&{auth_author}, not
${auth_author}).
${auth_author} is transient. If defined in the
configuration file or in the command line, that definition can be
ignored by sendmail.
