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

Sendmail has interfaces to three types of delivery agents. In verbose mode, Sendmail
reports its interactions with them as follows:
• Mailers that use SMTP to a remote host over a TCP/IP connection (IPC mailers).
In verbose mode, Sendmail reports the name of the mailer used, each MX host (if
any) to which it tries to connect, and each Internet address it tries for each host.
When a connection succeeds, the SMTP transaction is reported in detail.
• Mailers that run SMTP (locally) over pipes.
The name of the mailer used and the command line passed to exec() are reported.
Then the SMTP transaction is reported in detail. If the mailer returns an abnormal
error status, that is also reported.
• Mailers that expect envelope information from the Sendmail command line and
expect message headers and message body from standard input.
The name of the mailer used and the command line passed to exec() are reported.
If the mailer returns an abnormal error status, that is also reported.
Contacting the Sendmail Daemon to Verify Connectivity
It is possible to contact the Sendmail daemon and other SMTP servers directly with
the following command:
telnet host 25
Use this to determine whether an SMTP server is running on host. If not, your
connection attempt will return the message Connection refused.
After you establish a connection to the Sendmail daemon, you can use the SMTP vrfy
command to determine whether the server can route to a particular address. For
example:
telnet furschlugginer 25
220 furschlugginer.bftxp.edu ESMTP Sendmail 8.11.1/8.11.1; Wed, 28
Aug 2002 14:33:50 +0530 (IST)
vrfy [e-mail]
250 2.1.5 <[e-mail]>
vrfy [e-mail]
554 5.1.1 [e-mail]... User unknown
quit
221 2.0.0 furschlugginer.bftxp.edu closing connection
Connection closed by foreign host
Not all SMTP servers support the VRFY and EXPN commands.
94 Configuring and Administering Sendmail