We have been having the same issue with ATT.net. Our DNS is fine, including reverse lookup PTR and MX record. We've checked it with DNS Stuff and Men & Mice's DNS Expert utility.
Like previously reported, the 450 busy message is all that is received and not every e-mail receives it. Further, many times on a subsequent Queue run, ATT.net finally accepts the mail. Each of our customers have their own IP address. We receive e-mail to their domain and then forward it to their final destination POP at ATT.net. I'm wondering if ATT.net is doing some kind of rate limiting, i.e. only allowing a certain number of connections during a given period of time. Wednesday, March 1, 2006, 11:02:57 AM, Daniel Donnelly <[EMAIL PROTECTED]> wrote: DD> Only problem with Dave's conclusions is that the connection is DD> NOT being rejected/dropped. The 4XX errors indicate the server DD> does not have enough resources to handle a new message right now DD> and is asking the sender to try later when it should be DD> available. If ATT is not giving the right error response when DD> dropping the connect, then they are just plain wrong! But they DD> say the sender is not being blocked, which is consistent with the DD> error number Keith is seeing. DD> Why would one network get 95% failure and another does not? Good DD> question! If the connection attempt is made very close to the DD> same point in time and the responses are different, I have no DD> explanation except there may be some preference given to the DD> connection for one network over the other. Now this is not DD> supposed to happen, but I seen a few proposals to do just this DD> (paying more for premium network service). ATT is big enough to DD> be experimenting with something like this... DD> Maybe you can tell us here when you are seeing connection DD> problems and we can try connecting from our networks. If we all DD> try at some specific moment, we could cause a fair number of DD> connections and push their server a bit. If we also get the DD> error, well that confirms the problem is at their end, not yours! DD> You might try the other hosts in att's MX records to see if they DD> accept your email. You can force this by putting the IP & DD> hostname (att.net) in the HOSTS file on the IMail server, and DD> this will bypass the DNS lookups. If the other server accepts DD> your messages at a higher rate, well, that seems to confirm the DD> problem is the receiving mail server. DD> Daniel Donnelly DD> -----Original Message----- DD> From: [EMAIL PROTECTED] DD> [mailto:[EMAIL PROTECTED] Behalf Of Dave DD> Doherty DD> Sent: Wednesday, March 01, 2006 11:33 AM DD> To: [email protected] DD> Subject: Re: [IMail Forum] 450 busy, when delivering to att.net DD> Hi, Keith- DD> In my experience, most oddball problems with mail are DNS-related DD> in some DD> way. >> But I've specifically tried sending tests from domains that DD> are NOT using >> the gateway and these still get the '450 busy' response. DD> How are you sending the telnet from the domains? Does each domain DD> have its DD> own mail server? DD> One idea: See if you can get the gateway provider to try the DD> telnet test DD> directly on the gateway server. You may want to try using your DD> inbound DD> gateway also as an outbound gateway if you find that telnetting DD> from the DD> gateway works. DD> Second idea: Do you have SPF records for the domains? Are they DD> correct? DD> One way this MIGHT work: DD> - You start the telnet session DD> - ATT checks reverse lookup on your mail server's IP DD> - ATT tries a forward lookup on the returned FQDN to see whether DD> it matches DD> the IP DD> - ATT checks for an MX record covering the domain and looks to DD> see whether DD> that returns the IP DD> - ATT checks for an SPF record to see whether the IP is DD> authorized. DD> ATT MIGHT reject the connection if one or more of the following DD> are true: DD> - There is no reverse lookup for the IP DD> - There is a reverse lookup but the FQDN doesn't resolve to the DD> IP DD> - There is no MX record for the domain DD> - There is an MX record, but it doesn't resolve to the IP DD> - There is no SPF record DD> - There is an SPF record, but the IP isn't authorized DD> Just a few thoughts. There are certainly other explanations. DD> -d DD> ----- Original Message ----- DD> From: "imail" <[EMAIL PROTECTED]> DD> To: <[email protected]> DD> Sent: Wednesday, March 01, 2006 11:12 AM DD> Subject: Re: [IMail Forum] 450 busy, when delivering to att.net >> Dave and Matti, thanks for your ideas; they got me DD> thinking/testing in >> some new directions, but I'm still pretty stumped. >> >> Regarding the possibility of greylisting: "does the email DD> deliver with the >> next queue run?" No. Our mail server makes 5 attempts over DD> the course of >> several hours and usually all 5 attempts return the '450 busy' DD> smtp >> response. >> >> Regarding our MX records: we are using a third party spam DD> filtering >> gateway for inbound mail on some domains, but not all domains. DD> I hadn't >> thought of this being a potential problem before. But I've DD> specifically >> tried sending tests from domains that are NOT using the gateway DD> and these >> still get the '450 busy' response. >> >> To add to the mystery, I've discovered that the connections DD> aren't failing >> 100% of the time. The connections are failing roughly 95% of DD> the time. >> About one out of every twenty attempts are delivered fine. DD> When I try to >> telnet to att.net's smtp servers from our mail server >> (mail.addisontech.com), I get the exact same result: 95% of the DD> attempts >> return '450 busy', while 5% connect fine. >> >> Telnet from my workstation (on a different IP address, but in DD> the same >> Class C IP range) results in 95% failure (450 busy). Telnet DD> from my home >> computer (through a completely different ISP) results in 100% DD> success. >> Coupled with the tests Dave ran, I'm not sure what to make of DD> these >> results. AT&T continues to assure us that our mail server IP DD> is not being >> blacklisted. >> >> -Keith >> >> >> DD> To Unsubscribe: DD> http://www.ipswitch.com/support/mailing-lists.html DD> List Archive: DD> http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ DD> Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/ DD> To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html DD> List Archive: DD> http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ DD> Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/ ---- Don Brown - Dallas, Texas USA Internet Concepts, Inc. [EMAIL PROTECTED] http://www.inetconcepts.net (972) 788-2364 Fax: (972) 788-5049 ---- To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/
