or use the telnet port 25 command to test.
on the problem server try to telnet mailhost 25
like so
root@webby # telnet mailhost 25
Trying 172.42.203.252...
Connected to aquarius.
Escape character is '^]'.
220 aquarius.mydomain.com ESMTP Sendmail 8.8.8+Sun/8.8.8; Fri, 15 Dec 2006 11:10
:28
mail from:
sparcguy@mydomain.com <<------------------------ you type
anything@anything.com is fine
250
sparcguy@mydomain.com... Sender ok
rcpt to:
sparcguy@mydomain.com <<<------------------------ you must type a real email address
250
sparcguy@mydomain.com... Recipient ok
data <<< --------------------------------------------------- you type this
354 Enter mail, end with "." on a line by itself
test test <<< --------------------------------------------------------- you type these
. <<< -------------------------------------------------------- you type this
250 LAA29397 Message accepted for delivery
quit <<< -------------------------------------------------- you type this
221 aquarius.mydomain.com closing connection
Connection closed by foreign host.
root@webby #
250 LAA29397 Message accepted for delivery
if you cannot see this part
Connected to aquarius.
Escape character is '^]'.
220 aquarius.mydomain.com ESMTP Sendmail 8.8.8+Sun/8.8.8; Fri, 15 Dec 2006 11:10
:28
or you see dark blank screen, means either network routing problem, if you get immediate "connect close" after issuing telnet mailhost 25 it probably means remote mailhost smtp port 25 is blocked by maybe a firewall in between, or smtp services like sendmail on remote server not started.