Cannot send E-mail to Certain Domain

[Joefederico]

Hoping someone can help with this prob. A customer of ours has there email hosted by a web provider and everything we send to them sits in our IMS queue and eventually an NDR is received by us. I can ping the mail server by name and IP. I can also connect via Telnet so, I'll assume, it's not a router or firewall problem on my end. Can receive email from them as well. I'm thinking I need to tweak something on my Exchange Server but everything I've tried has not worked. Thanks in advance!

 

[dennisbbb]

You need to change the DNS server entries on the Exchange Server. Basically the current entries bring you to a DNS server that has no more records of the domains you want to send to.

 

[Joefederico]

Dennisbbb

But if that were the case I wouldn't be able to ping them by name or telnet into their mail server...correct? Both of which I can can currently do.

 

[dennisbbb]

I know what you mean. Ping and Tracert review no problem. You can even resolve the domain name to ip. But strange as it is, give it a try.

I had this problem before and all it took was a change in DNS number. In my case, I simply switched around my Primary and Secondary numbers under TCP/IP settings and voila everything works till this day.

 

[Joefederico]

I already started the process of getting in touch with the ISP and re-confirming their DNS servers, as well as re-arranging the DNS search order in an attempt to either resolve the problem or eliminate it as a possible cause.

Appreciate your follow-up...thank you. Crosing my fingers and will re-post the results...hopefully good!

 

[Joefederico]

I've confirmed with ISP on DNS servers. They are all up to date. Changed the order twice with no further luck. Still cannot send to them. Apparently, the rest of the world can but me.

Any other ideas? This is really ridiculous.

 

[dennisbbb]

You can try other isp's DNS servers. That's the only thing you can do. Try find Earthlink, AT$T, Covad, Charterpipeline DNS numbers.

There are no other problems with your server.

One other possibility is they may have blocked port 25 on your ip block. This will prevent you from sending them any email.

 

[mike722]

One thing you may need to think about is reverse DNS. Does your own domain have reverse DNS records on your ISPs DNS server? The domain you are trying to send to may being checking reverse DNS querys to stop spam. When they get an email, their mailserver will check the ip address of the server (your mailserver), so a reverse DNS to see what domain is assoiciated with the ipaddress and then see if it matches the domain of the senders email. If it matches, they accept the mail, if it doesn't, they don't allow the mail in, if no reverse DNS record can be found, it rejects the connection. I could be wrong , but it's worth considering.

Mike

 

[Joefederico]

Thanks for the good ideas. Confirmed we have reverse DNS. I eventually "resolved" the problem by putting the IP address and name of their mail server in our Exchange's Hosts file. They change their IP or email address it'll be a problem but at least they can send email to this site now.

Thanks again for your input...greatly appreciated.