My employer hosts his own exchange 2003 SMTP server, which typically works without problems. Over the past month or so, we have seen emails to two domains fail to arrive at their destinations. have sent test emails to known good addresses in these target domains and then monitored the messages using MS Exchange Server 2003's email tracking function. A couple days after the message is queued for remote delivery, I see a very long list of retries like: smtp: message transferred to *******.bigfish.com through SMTP. Note that if I do a mx lookup of the target domain, I see: MX preference = 15, mail exchanger = Mail.Global.Frontbridge.com And then if I telnet to frontbridge, I see one of the bigfish addresses similar to the ones in the message tracking (retries, I guess): telnet Mail.Global.Frontbridge.com 25 220 DB3EHSMHS009.bigfish.com Microsoft ESMTP MAIL Service ready at Sat, 19 Feb 2 011 17:07:36 +0000 At the moment, the problem has gone away and we can send to the target domain again. However, I have noted something which I don't understand. The most common mx responses to nslookup seems to look like this: #nslookup Default Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 > set q=mx > microsoft.com Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 Non-authoritative answer: microsoft.com MX preference = 10, mail exchanger = mail.messaging.microsoft.com But, if I do the same thing with our domain, I see a different result: #nslookup Default Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 > set q=mx > mycompany.com Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 mycompany.com primary name server = ns1.biz.myisp.com responsible mail addr = dnsadmin.myisp.com serial = 2008122312 refresh = 3600 (1 hour) retry = 604800 (7 days) expire = 3600 (1 hour) default TTL = 0 (0 secs) Note that our email (smtp and pop) are working just fine today, and seem to usually work OK. We have not recently requested any dns changes or updates from our provider--neither when the problems started, nor when they went away. But I don't expect this means our DNS records are "correct"; only that if something is wrong, the problem is only exposed under certain conditions. Does the nslookup mx response produced for mycompany.com indicate there is something wrong? Is "responsible mail address" = something.ourisp.com a legitimate response if we're hosting our own POP and SMTP servers? I suspect these are fairly fundamental questions, and would be grateful if somebody could explain to me what the response should look like--or better yet, point me to a resource where I could study these things myself. I've been looking around google, wikipedia, and MS, and am running into such an abundance of information that I'm having trouble finding the answer to my small question! Thanks to anybody who can help me educate myself.

It depends on who owns your DNS records. You should talk to your ISP's support staff to ensure that everything is set up properly.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

We are having the same issues with a domain. When doing a NSLookup I get the "responsible mail addr" response instead of the MX records also. I came across an article about NT that said if you add a period to the end of the domain it will show it properly. I did this and it worked. here is the difference of the NSLookups > osu.edu Server: ns1.net.ohio-state.edu Address: 128.146.1.7 osu.edu primary name server = ns0.net.ohio-state.edu responsible mail addr = hostmaster.osu.edu serial = 287548132 refresh = 21600 (6 hours) retry = 10800 (3 hours) expire = 604800 (7 days) default TTL = 10800 (3 hours) and now with the period > osu.edu. Server: ns1.net.ohio-state.edu Address: 128.146.1.7 osu.edu MX preference = 10, mail exchanger = defang2.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang3.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang4.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang8.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang11.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang12.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang13.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang14.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang15.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang16.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang17.it.ohio-state.edu osu.edu MX preference = 10, mail exchanger = defang18.it.ohio-state.edu osu.edu nameserver = ns2.net.ohio-state.edu osu.edu nameserver = ns1.net.ohio-state.edu osu.edu nameserver = ns3.net.ohio-state.edu defang2.it.ohio-state.edu internet address = 128.146.216.82 defang3.it.ohio-state.edu internet address = 128.146.216.83 defang4.it.ohio-state.edu internet address = 128.146.216.84 defang8.it.ohio-state.edu internet address = 128.146.216.89 defang11.it.ohio-state.edu internet address = 128.146.216.18 defang12.it.ohio-state.edu internet address = 128.146.216.21 defang13.it.ohio-state.edu internet address = 128.146.216.127 Do you see the mx record if you add the period at the end of the domain?

Thanks, Ed, for your answer--I have asked our team to follow up with the ISP. Thanks, Roland--I tried appending a dot. I get the same thing by adding the trailing dot, which suggests that we really don't have a "preferred mx" listed. Ed seems to suggest this MIGHT be OK or it might not--we will find out from the ISP, I hope. Also, a rDNS check looks like it should work BUT--something I don't understand--maybe it's not strictly correct and most servers just let it slide most of the time. That's a different question. When I try mxtoolbox.com, I see my company's web server and their mail server: Now, I am guessing this proves my "preferred mx" is implicit because it's the mx directly at at "mycompany.com". I can find my mx--but I have to do 2 searches--first find the IP, then see who is using it. Somebody tell me why (if) I can't draw that conclusion from the information I have here; I will thank you for it! mxtoolbox.com says... ptr:###.###.###.### ptr Type IP Address Domain Name TTL PTR ###.###.###.### mail.mycompany.com 24 hrs PTR ###.###.###.### www.mycompany.com 24 hrs reverse lookup smtp diag port scan blacklist Reported by 24.30.201.19 on Sunday, February 20, 2011 at 8:26:35 AM (GMT-6) and with the trailing dot I see... Microsoft Windows XP [Version 5.1.2600] (C) Copyright 1985-2001 Microsoft Corp. #nslookup Default Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 > set q=mx > mycompany.com. Server: 44.sub-66-174-95.myvzw.com Address: 66.174.95.44 mycompany.com primary name server = ns1.biz.myisp.com responsible mail addr = dnsadmin.myisp.com serial = 2008122312 refresh = 3600 (1 hour) retry = 604800 (7 days) expire = 3600 (1 hour) default TTL = 0 (0 secs)

Hi, It's the DNS issue. The result is retrieved from the DNS that the Exchange Server is using. AllenAllen Song

Allen, thanks for your comment. Can you point a poor newbie in the right direction with a more specific suggestion? What is the DNS issue you're referring to? As I continue to read about MX records (faqs.org, ietf.org), it seems my MX record (if I had one) would be involved in routing incoming mail--which seems to be getting through. DNS resolves (both fwd & reverse) mail.mycompany.com, mycompany.com to our expected IP address. But there is no MX record for mycompany.com in DNS. Are you saying that my "MX preference" must necessarily be published in DNS for outgoing mail to work? Or does that requirement depend on the ISP? Is there a different DNS issue you're talking about here that affects outgoing mail? Thanks very much for your advice!

It depends on who owns your DNS records. You should talk to your ISP's support staff to ensure that everything is set up properly. Ed Crowley MVP "There are seldom good technological solutions to behavioral problems." Thanks, Ed. We have spoken with our ISP, and they say we don't need an MX record. We host our own email server and have only one public IP address. So internet mail to our domain has only 1 possible place to go. We had them add an MX record anyhow, as they said it wouldn't hurt, and it has been suggested that there is a problem in DNS.

Hi, It's the DNS issue. The result is retrieved from the DNS that the Exchange Server is using. Allen Allen Song Thanks, again, Allen--Since my last question to you, we have added an MX preference record. Is this what you're talking about as the DNS issue? Or is it something else?