HP-UX Mailing Services Administrator's Guide (B2355-91064)

Support for Deliver By SMTP Extension (RFC 2852)
The Deliver By SMTP extension is a mechanism by which an SMTP client requests a
server to deliver the message within a specified period of time, while transmitting a
message to an SMTP server. A client that makes such a request also specifies the message
handling that 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
configuration file:
#O DeliverByMin=0
A value of 0 (zero) indicates that the DeliverByMin option is disabled. You must 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. The DeliverByMin option expresses the urgency of a message and provides
an additional degree of determinacy in its processing. The message can be withdrawn
if it is not delivered within the specified period of time.
This mechanism is used to prevent the delivery of a message beyond some future time
of significance to the sender or recipient, but not known by the MTAs handling the
message.
It can also be used to alert a sender about delivery delays. In this case, the sender can
mark a message so that if it is not delivered, for example within 30 minutes, a "delayed"
DSN is generated, but the delivery attempts continue nonetheless. Senders are allowed
to express a preference for receiving alerts.
Support for RFC 1413 (Identification Protocol)
identd is a server that implements the TCP/IP proposed standard IDENT user
identification protocol as specified in RFC 1413. identd listens on port 113 and operates
by looking up specific TCP/IP connections and returning the user owing the process
owning the connection.
Sendmail uses identd as an advisory mechanism to log the identity of the user name
and host name of the Sendmail client. identd may cause additional traffic for collecting
the user name, which may adversely affect the performance of Sendmail.
Enabling identd on the Sendmail Server
You can enable identd on the Sendmail server by uncommenting the following entry
in the /etc/mail/sendmail.cf file:
#O Timeout.ident=5s
By default, the identd timeout value is 5 seconds.
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