||V8.10 and above
RFC2554 describes the currently approved method for SMTP
authentication. One part of this method is to add the AUTH= extension
to the MAIL FROM: command for ESMTP. This A line
in the qf file is used to store the value passed
in that parameter.
If you compiled sendmail with SASL defined
(SASL), this value will be the actual value
passed by the AUTH=. Otherwise it is the value of
$f ($f) normalized to
the local domain if $f lacks a domain.