The -N command-line switch causes sendmail to append the DSN NOTIFY command to the ESMTP RCPT command. For example:

RCPT To:<friend@other.site> NOTIFY=SUCCESS

Here, sendmail is requesting that the other site return notification of successful delivery.

The -N command-line switch also causes sendmail to behave as if it got the NOTIFY command when producing a local bounce message. That is, -N affects the other sites' behavior on SMTP mail, and the local site's behavior on local delivery.

Should the message be successfully delivered by a host that understands DSN, or by the local host, a return message will be sent to the sender. If either site is running V8.8 or above sendmail, that return message will look (in part) like this:

Date: Fri, 13 Dec 2002 08:11:43 -0800 (PST)
From: Mail Delivery Subsystem <MAILER-DAEMON>
Subject: Return receipt
Message-Id: <200212132144.f21IuJf8029510@other.site>
To: <you@your.site>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
        boundary="f21IuJf8029510.834702270/other.site
Auto-Submitted: auto-generated (return-receipt)

This is a MIME-encapsulated message

--f21IuJf8029510.834702270/other.site

The original message was received at Fri, 13 Dec 2002 08:11:43 -0800 (PST)
from other.site [204.255.152.62]

   ----- The following addresses had successful delivery notifications -----
friend (successfully delivered to mailbox)

The -N command-line switch tells the NOTIFY command what to include and thus tunes how notification will be handled. The form of the -N command-line switch looks like this:

-Nnever
-Nkeyword,keyword,...

The first form sets NOTIFY to be NEVER, meaning send no notification. The second form tells NOTIFY to specify notification based on one or more of three possibilities:

success

The success keyword tells sendmail to ask for notification of successful final delivery.

failure

The failure keyword tells sendmail to ask for notification if the message fails to be delivered.

delay

The delay keyword tells sendmail to ask for notification if the message is delayed for any reason.

These keywords can be listed after the -N to set a combination of notification requests. For example:

-Ndelay,success

This tells sendmail to ask for notification if the message is successfully delivered or delayed but not to get notification if the message fails.

If an unknown keyword is listed, sendmail prints the following error message and ignores the bad keyword:

Invalid -N argument

If the -N command-line switch is omitted, notification policy is left to the other site. The usual default is failure (and possibly delay). On the local machine, sendmail acts as though both failure and delay were specified.