Hi, for some reason today, we can't send emails out to Yahoo, AOL and Comcast. We have no issues in sending out emails to many other domains. We had no issues in sending out emails to the three above domains yeatrday or the day before or a week ago. We did not change anything. When I check the queues, I see the server tries to send emails to the domains. Sometimes I get "unable to bind to the destination server in DNS" and sometimes I get the remote server did not respond to a connection attempt. I checked with my ISP and their DNS servers are online and with no issues. I try to force the connection but that dose not help. What do I need to check to see if this is an issue from our server, the ISP DNS servers or the domains I'm trying to send emails out to? Thanks

All three of those providers operate their own blacklists, so there is always a chance that you have got listed. No public way of querying the lists unfortunately. Have you tried a manual telnet test to the MX record host to confirm connectivity? http://dosprompt.info/mx-example.asp Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

Thanks Simon. I don't think that we are blacklisted because we were able to send emails to them yeaterday. When I do nslookup from the server itself to any of these three I get "DNS request timed out" I can get nslookup information on many other sites. I can telnet to port 25 from the server fine to AOL, Yahoo and Comcast. Any idea what might be the issue? I wonder whay I can't do an NSlookup from the server to these 3 Thanks

The fact that you could send email to them yesterday and can't today doesn't mean you aren't blacklisted. Blacklists are not static. They are very dynamic. It would appear to be a DNS issue. How is your DNS configured? It should be that the only DNS servers in the network configuration are the domain controllers. Are you then use root hints on the domain controllers or forwarders? Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

This is very strange because right now, nothing in the queues and all messages were delivered fine. Now when I send message to AOL, Yahoo or Comcast, they get delivered instantly with no issues or retries. Again, have not changed anything at all. This is the only server we have, it is the AD, DC, DNS and Exchange server (SBS 2003). Now I can use NSlookup from the server itself to get records for yahoo. aol, etc. There must be something with the DNS server but I can't figure it out. Anything I should check for? Thanks again

After the event it is hard to know. It could have been issue with your ISP, which they will never admit to. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

As you said. I called them and they said they had no issues with their DNS servers. I still want to know what really happened. Since then, all emails are getting out fine with no issues.

The fact that the ISP said they had no issues doesn't mean they didn't have an issue. ISP tech support routinely lie about issues. This is either because they are told to, or the fact that first line support aren't aware of any problems. I have presented ISPs with evidence of issues which they have refused to acknowledge in the past. I use ISPs now connectivity only. I don't use their DNS, their SMTP gateways, their domain name services etc. As the issue is now resolved, there is no way of knowing what the original problem was. If you didn't change anything then it is likely to be something outside of your network. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources