HP-UX Mailing Services Administrator's Guide

Sendmail 8.13.3
New Features in Sendmail 8.13.3
Chapter 3 117
Support for Deliver By SMTP Extension (RFC 2852)
The Delivery By SMTP extension is a mechanism by which an SMTP
client can request a server to deliver the message within a prescribed
period of time, while transmitting a message to an SMTP server. A client
that makes such a request also specifies message handling which must
occur if the message cannot be delivered within the specified time period.
The options can be either to return the message as an undeliverable
message with no further processing or to issue a delayed delivery status
notification (DSN).
Following is the declaration for the Delivery By SMTP extension in the
Sendmail 8.13.3 configuration file:
#O DeliverByMin=0
A value of 0 (zero) indicates that the DeliverByMin option is disabled.
Do not consider this extension as a vehicle for requesting “priority”
processing. A receiving SMTP server can assign processing priority to a
message transmitted with a Delivery By request. A Delivery By request
serves to express the urgency of a message and to provide an additional
degree of determinancy in its processing. The message can be withdrawn
if it is not delivered within the specified period of time.
A typical usage of this mechanism is to prevent delivery of a message
beyond some future time of significance to the sender or recipient but not
known by the MTAs handling the message.
Another common usage arises when a sender wishes to be alerted to
delivery delays. In this case, the sender can mark a message such that if
it is not delivered, for example within 30 minutes, a "delayed" DSN is
generated but delivery attempts are nonetheless continued. In this case,
senders are allowed to express a preference for when they would like to
learn of delivery problems.
Anti-Spamming Features
In addition to the anti-spamming features provided by Sendmail 8.11.1,
Sendmail 8.13.3 provides the following anti-spamming features:
• Message quarantining
• Support for mailer filter (MILTER) APIs for advanced and effective
mail filtering
• Enhanced DNS Black Hole List (EDNSBL) option