You can see the mailer, host, user triple sendmail will deliver a message to a recipient by using the "/parse" command in address test mode:

      sendmail -bt
      ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
      Enter <ruleset> <address>
      > /parse user@some.dom
      Cracked address = $g
      Parsing envelope recipient address
      canonify           input: user @ some . dom
      .
      .   (output deleted)
      .
      final            returns: user @ some . dom
      mailer relay, host smtprelay.foo.com, user user@some.dom

The "mailer" is the delivery agent that will do the actual delivery. You can find it in your sendmail.cf file by looking for the line starting with"Mmailername", in this case "Mrelay". The relay mailer is an ESMTP mailer that allows 8 Bit data with out any correct MIME labeling.

The "host" is the host that sendmail will connect to, in this case an SMTP relay "smtprelay.foo.com".

The "user" is the actual recipient address that will be passed to the next host for delivery, in this case "user@some.dom"