Locating the Correct Mailer:

The other variable that determines the rulesets used to process an address is the mailer. To find out which mailer delivers the mail, run sendmail with the -bv argument:

#$ sendmail -bv craig@wrotethebook.com
craig@wrotethebook.com... deliverable: mailer esmtp, host
wrotethebook.com., user craig@wrotethebook.com

To see which mailer is used to deliver mail to remote sites, run sendmail with the –bv argument, and give it a valid e-mail address for the remote site. In the example, the address is craig@wrotethebook.com. sendmail displays the mail delivery triple returned by ruleset parse: the mailer, the host, and the user. From this, you know that the mailer is esmtp.