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Can't telnet to smtp server outside of network

Posted on 2011-03-09
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Having issues with 2010 exchange and getting mail to go out, so i tested from the exchange server telnet on port 25 to a mailserver, and it times out, it resolves with nslookup and responds to ping, just won't telnet,  so i thought, ok, ill try from a different machine, same thing, all workstations can't telnet out on port 25, looking at firewall rules etc and notice they have a gpo of some sort dealing with the firewall.  Could that be the problem or is it a router issue possibly?
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Question by:jasonmichel
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Tasmant earned 668 total points
ID: 35083582
i don't think it's linked with your router as you can ping outside computers. therefore we need to consider that you are well NAT translated.
but we can clearly suppose your firewalls rules don't allow you to go out on port 25, which is an issue, especially for your Exchange server (could be good for computers).
maybe could you be clearer with "gpo of some sort dealing with the firewall" if you want to get more details ? :)
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by:Alan Hardisty
Alan Hardisty earned 668 total points
ID: 35083599
The other option that is possible is that your ISP has port 25 blocked outbound as an anti-spam measure, but you would need to rule out your firewall as the problem first before beating on the door of your ISP.
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by:Suliman Abu Kharroub
ID: 35083607
Please test smtp on http://mxtoolbox.com

if it fails, check the exchange services...information store...
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by:GundogTrainer
ID: 35083998
alanhardisty sounds the most plausable explanation if your having the issue on all clients.

I would try and telnet to the SMTP server of your ISP as if you were using a standard mail client.
If that works then its most likely your ISP preventing users from spamming and you may need to forward mails through this smarthost rather than deliver direct.
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by:GundogTrainer
ID: 35084017
Forgot to ask, can you telnet to port 25 on your exchange server from a local client ?
This would test if it was a possible GPO \ client firewall iss or is at or beyond the gateway.
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by:Marius Gunnerud
ID: 35084212
from your smtp server go to http://canyouseeme.org/ enter port 25 and see if the port shows as open
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by:Alan Hardisty
ID: 35084241
The question states:

"Having issues with 2010 exchange and getting mail to go out"

How is checking the inbound port going to help?
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by:jasonmichel
ID: 35084317
I can telnet into my exchange from inside and outside fine
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by:Alan Hardisty
ID: 35084328
Did this work before and recently it stopped?
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by:jasonmichel
ID: 35084531
Fresh exch 2010 install...so hadn't had to test before....never had issues with send connector to inet before...usually pretty simple
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by:Alan Hardisty
ID: 35084587
Have you sent mail out from your IP before using port 25?
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by:jasonmichel
ID: 35084642
Yes from an icewarp server we are currently migrating from
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by:Alan Hardisty
ID: 35084686
Is the Icewarp server still connected?
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by:jasonmichel
ID: 35084718
I believe so, but dns internally has been changed and the statements in router have been changed
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by:Alan Hardisty
ID: 35084732
Ah - okay - I was just thinking about changing the IP of a client to that of the Icewarp box and testing telnet from there.

Sounds like the router changes got messed up.

Can you check them please - seems the most logical place to check.
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by:jasonmichel
ID: 35084796
I can telnet from outside to exchange fine?
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by:GundogTrainer
GundogTrainer earned 664 total points
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I think what alanhardisty meant was there may be an IP filter on the router to block port 25 from everyone except the mail server.
You have updated the port forwarding rule for inbound traffic, but is there an outbound filter applied ?
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by:Alan Hardisty
ID: 35084875
Yep - that's what I meant.

If you could send out before the changes to the router on the Icewarp IP - try setting a PC up as the same IP and test with Telnet.  If that works - you know the issues is a firewall / router issue.

If not - then it is still probably the router / firewall.
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by:Tasmant
ID: 35094062
that's what i said in the first answer ...
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