I set up a script on one server, lets call it "A" to be able to 'ping' (open and close a connection on) a second server "B" on several critical ports (i.e. 25, 80...) to check for active services.
So server A is opening connections to server B frequently on several ports and it's working like a charm... until suddenly port 25 (exim) stops reponding to server A. It still works from every other computer.
I have searched (grep) /etc and /var/log and there are no indications that the ip address was blocked from there.
So my question is: where is exim or another system component blocking server A?
serverA[root]# telnet serverB.com 25
telnet: Unable to connect to remote host: Connection refused
C:\myHomePC>telnet serverB.com 25
220-serverB.com ESMTP Exim 4.34 #1 Mon, 05 Jul 2004 20:56:23 -0400
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.