The $b macro contains
the current date in ARPAnet format, as defined in RFC822, section
5.1, and amended by RFC2822, section 3.3.
Because $b holds the current date and time,
sendmail frequently updates the value in that
macro. When sendmail first starts to run, it
places the current date and time into $b.
Thereafter, each time an SMTP connection is made and each time the
queue is processed, the value of the date and time in that macro is
If the system call to time(3) should fail, the
value stored in $b becomes Wed Dec 31 15:59:59
1969, and no other indication of an error is
$b is chiefly intended for use in
configuration-file header definitions that require ARPAnet format
(such as Received:, Received:).
$b is transient. If it is defined in the
configuration file or in the command line, that definition can be
ignored by sendmail. Note that a
$& prefix is necessary when you reference this
macro in rules (that is, use $&b, not