Beginning with V8.12, sendmail supports the
DELIVERBY SMTP extension (defined by RFC2825). If the
DeliverByMin option (DeliverByMin)
was defined with a positive value, a BY= equate
can follow the SMTP MAIL FROM command for inbound email. The
BY= equate defines the window of time during which
the message should be delivered. That equate's time
value can optionally be followed by a flag that states what to do
upon delivery (an r flag), or upon delivery
failure (an n flag). There can also be a flag that
advises sendmail to trace delivery (a
v flag). The BY= information is
saved in the qf file on an !
line:
!flag time
Here, the time is the time specified by the
By= and the flag is a
one-byte integer that encodes a value of 1 (notify the sender upon
delivery), or 2 (return the message if it cannot be delivered in
time). Additionally, the flag can be
OR'd with a 0x10 (trace the delivery).
This ! line appears for inbound mail only, and
appears only if you have configured your mc file
to define the DeliverByMin option with a positive
value.
