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Sending email over internet

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by cnaes

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Users at my company cannot send email to another company over the internet. However we can receive email from them. I did a tracert and can only get halfway to the company (to their ISP), then I get "Request timed out". I used trace software thatstates that ICMP is blocked at their ISP. Can anyone tell me --- Does the problem have anything to do with ICMP being blocked? And if not, any other ideas why we can receive email from them, but cannot send email to them? We have no other problems with email.

Thanks in advance for your help.

13 replies

by fcrammond

Ping and tracert both use the ICMP(internet Control Messaging Protocal) and can be blocked. Recent "denial of services attacks" were caused by crackers using icmp related services, so icmp has been bloced by some companies. I recently had a problem much like yours. The tech at that company said that we had an open port. So I changed the Routing to "Do not reroute incoming SMTP mail" and the company could then recieve email from us. Hope this helps.

by cnaes

Thanks for your help. Surprisingly this problem turned out to be a setting on my firewall.

by cnaes

I did an nslookup type=mx on two of the domains I'm trying to reach and it returns our old email server's name and address rather than our new email server information. So, is there a way on my end to correct this?

by joseph moore

Ok. First off, being able to PING someone and send them e-mail are not specifically related. As Answer1 states, a lot of places are blocking ICMP packets. Many firewalls now suppress ICMP from passing through it to reach its protected servers, due to DoS attacks. Yet, just because you can't ping a domain doesn't mean you can't e-mail it either.
Now, if the domain was down (their servers were offline, their firewall was down, etc) then yes, you couldn't PING them or e-mail them. But, let's not focus on that. That is an extreme reason for your problems.
Now, if you saw a misconfiguration in the MX records doing an NSLOOKUP, then that could be the problem.
Ok, make sure their MX records are correct. Do another NSLOOKUP against your DNS servers (either your own DNS servers, or the DNS servers your ISP provides), and check if the FQDN and/or IP address supplied for this other domain is correct. If you know what the IP address for this domain is, then is the IP in the MX record right?
Another thing to check is try and traceroute to this IP address also. Again, it might not work, but you can try.
Also, try and go to a web site on that IP address. Just put the IP address you get from the MX record in your web browser (with HTTP:// in front of the IP) and see if it points to the other company.
Also, check your mail server, see if it has the correct DNS settings. Make sure the DNS server can resolve the IP address to the FQDN in the MX record.
Lastly, call the other company and see if they are having trouble.

by joseph moore

And the very last thing to try (if you are REALLY desperate) is try and TELNET to their mail server's SMTP port.
For example, say the MX record for this company points to 10.1.1.1 (it won't' but this is just an example). Open up a Command Prompt and type in:
TELNET 10.1.1.1 25

That will attempt to establish a Telnet session with the SMTP port at that IP address.
And if you get something remotely similar to this:

220 mail.theothercompanydomain.com ESMTP 3.52 (build 1375) ready at Mon, 19 Aug 2002 17:28:06 -0500

Then you will know they can receive e-mail, since the SMTP port (port 25) is open.

Good luck.

by cnaes

Thanks for your help. Surprisingly this problem turned out to be a setting on my firewall.

by some guy in seattle

ICMP isn't an issue, and isn't related to delivery of SMTP. These symptoms (and your added note confirmed it) indicate a reverse DNS look-up issue. The other company's SMTP server is trying to do a reverse lookup to your SMTP server's IP and is getting a different name. To fix this, make sure the reverse zone information on your public DNS server is set properly for your SMTP server (if you don't manage your public DNS info, call your ISP).

The issue by poster number one sounds more like it relates to mail relaying - a popular way for spammers to propagate mail through an open SMTP gateway. Blocking relaying prevents the mail server from handling mail for domains it is not responsible for.

Hope that helps -

by cnaes

Thanks for your help. Surprisingly this problem turned out to be a setting on my firewall.

by cnaes

The company is able to Telnet to our email server and we are able to email them as well. In response to answer 1, I am unable to turn off "Reroute incoming SMTP mail) as we are also using POP. Since we can both telnet, it seems like an Exchange config problem, but I don't know on whose side and/or what else to check.
Thanks again for your help

by cnaes

surprisingly this problem turned out to be a setting on my firewall. Thanks for your help

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