sendmail, 4th Edition

$b

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The current date in RFC2822 format

All versions

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 updated.

If the system call to time (3) should fail, the value stored in $b becomes Wed Dec 31 15:59:59 1969, ^[14] and no other indication of an error is given.

^[14] The actual time depends on the local time zone.

$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 $b ).