Mailing List Message #96612
From: Urs Gruetzner <>
Subject: Re: CGP SMTP Server frequently not available
Date: Sun, 2 Nov 2008 16:20:59 +0100
To: CommuniGate Pro Discussions <>
X-Mailer: CTM PowerMail version 5.6.2 build 4501 German (PPC) <>
Thanks again for your kind help. I will tell him to do this telnet test

Question: As the error is not happening 100% (There are times when he
CAN send the mails through our server) is it possible that the
redirecting by the ISP is also only random?


From: Tom Rymes <trymes>
Subject: Re: CGP SMTP Server frequently not available
Date: Sun, 2 Nov 2008 08:48:27 -0500
To: "CommuniGate Pro Discussions" <>
X-Mailer: Apple Mail (2.753.1)

On Nov 2, 2008, at 3:17 AM, Urs Grützner wrote:

Thanks for the answers

He is not in China, but living "in the pampa" in Thailand, connecting
with a radio modem, I guess EDGE.

When sending from Yahoo, he uses webmail, according to the mail header.
When using our server, Thunderbird as Mail client.


Please have him connect to your SMTP server using telnet to port 25. You
can then check the greeting given by the server that answers to
determine if his ISP is intercepting all traffic on port 25 and sending
it to their mail server instead of yours. As I mentioned before, many
ISPs do this as a way to try and limit spam. For instance, if you
connect via AOL dial-up and try to send mail on port 25, you end up
connecting to the AOL SMTP server, not the one you specify in your
client settings.

Here is the output when connecting to my mailserver from a MacOS
terminal session:
dualie:~ trymes$ telnet localhost 25
Connected to localhost.
Escape character is '^]'.
220 ESMTP CommuniGate Pro 5.2.7 is glad to see you!


Type "quit" at that prompt to disconnect.

If you get something like "220 ESMTP", then his SMTP
traffic is being redirected to another server by the ISP. You need to
set an SMTP listener up on another port and have him specify that port
number in his client setup. Come to think of it, I think that CGP comes
configured out of the box to use 587 or some other port as an
alternative to port 25. You may have to forward that port to your server
if it is behind NAT.

Another example:

dualie:~ trymes$ telnet 25
Connected to
Escape character is '^]'.


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