The mconnect program opens a connection to a mail server on a host that you specify and enables you to test that connection. The program runs interactively, so you can issue various diagnostic commands. See the mconnect(1) man page for a complete description. The following example verifies that mail to the user name sandy is deliverable.
% mconnect phoenix connecting to host phoenix (172.31.255.255), port 25 connection open 220 phoenix.example.com ESMTP Sendmail 8.13.1+Sun/8.13.1; Sat, 4 Sep 2004 3:52:56 -0700 expn sandy 250 2.1.5 <firstname.lastname@example.org> quit
If you cannot use mconnect to connect to an SMTP port, check these conditions.
Is the system load too high?
Is the sendmail daemon running?
Does the system have the appropriate /etc/mail/sendmail.cf file?
Is port 25, the port that sendmail uses, active?