Exim is blocking an ip address

[elleryjh]

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?

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serverA[root]# telnet serverB.com 25
Trying bb.bb.bbb.bb...
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.

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[casey]

It's the pop before smtp setup. Your home computer is authorized because you have logged into pop before telneting to the smtp port.

[chirpy]

casey, I don't think it will be POP before SMTP. You should still always be able to connect to port 25 (anyone should), it just you won't be able to relay any email through the server without prior authentication.

elleryjh, do you have APF installed, or some other iptables firewall on either server? You could check both servers for blocked ip addresses with:

iptables -L -n | grep other-servers-ip-address

Do that on both servers. If that doesn't match have you perhaps enabled the WHM > Security Tweaks > SMTP Tweak on serverA.com which might be preventing outgoing connections on port 25 to anyone other than root and mailman, etc.?