I have a bizarre one that has me completely stumped. The problem is that we cannot send mail to ONE particular domain (acstechnologies.com) via our Exchange 2007 SP1 box running on Windows Server 2008. When sending to this domain, users get a Message Delayed 4.4.7 error and a day later get a final error that it could not be delivered.When I look in the Exchange 2007 Queue Viewer I indeed see:acstechnologies.com DNSConnectorDelivery Retrywith two messages stuck in the queue. My first troubleshooting step was to telnet (on the Exchange box itself) to port 25 at their MX record (mail.acstechnologies.com), which worked, so I went ahead and crafted a raw SMTP message and it got through to them just fine. This proves there is no firewalling or blacklisting going on, I think.My next troubleshooting step was to get out the packet sniffer and watch the DNS traffic as I did a "retry" on the messages stuck in the queue. This is where it gets weird... the packet traces show NO attempt at looking up the A record their mail server, but instead I see my DNS servers (both Win2008 as well) asking my ISP's DNS servers for AAAA *IPV6* records for this domain, which of course don't exist!I thought perhaps the A record was cached and that's why I wasn't seeing it on the wire, so I cleared the DNS server's cache, and also did IPCONFIG /FLUSHDNS on the Exchange box and tried again, but again I see NO lookup for any A record at the specific domain in question and only the bad lookups for nonexistent AAAA records. I posted here as I think this is an Exchange problem more than a Windows DNS one, since I was easily able to ping their domain, telnet to it, and send a raw message (all from the Exchange box) using the same DNS servers.Does anyone have ANY idea what might be going on? We've been running Exchange 2007 for nearly a year without issue, and all other domains (to date) are fine. It is only this ONE that we cannot send mail to.I am at my wits end!

Hi, First please try to check your Domain name with http://www.dnsstuff.com/ to see if it has been listed in the blacklist. Besides, please try to check if we can use other email address to send email to this domain. Please check if you have any spam filter. Document listing below has a detail explanation about error 4.4.7,you can refer to it. Troubleshooting Exchange Error 4.4.7 Delivery Delay and Failures http://thebackroomtech.com/2008/03/28/troubleshooting-exchange-error-447-delivery-delay-and-failures/ More related information share with you: http://www.intodns.com/acstechnologies.com Regards, Xiu

Xiu-Thanks for the info. I have done further troubleshooting on this issue, and this is what I know:- There is nothing wrong with the domain we are trying to send to- We are not on any blacklist- FROM my Exchange 2007 box, I can TELNET to port 25 on this problem domain and send a raw SMTP message, which goes through fine.- When I take a packet trace of my Exchange server trying to send a message to this domain, I see NO request at all for the A record of the remote mail server, but instead see a lookup for a AAAA (IPv6) record, which of course fails.- If I add the problem domain's mail server and address to my Exchange server's HOSTS file, messages get there just fine.So, what I am seeing is some bizarre problem where *Exchange* cannot look up this one particular domain correctly, but CAN when it finds it in the hosts file. Of course you would assume a DNS problem, but that does NOT explain how I am then able to telnet to the domain (via its hostname) and send mail manually just fine, using the SAME DNS to get there that Exchange is (or should be) using. I have also verified that Exchange is using the NIC's DNS server's, not different ones.I am completely stumped!

Hi, First lets try to clarify the issue. 1. Please check External DNS Lookups settings on Hub Transport Server. By default, it should be Use network card DNS settings.(Note: Exchange Management Console-Server Configuration-Hub Transport-Properties). 2. Please collect netmon on Exchange Server and DNS server and send these file to me. 3. Please run ipconfig /all on Exchange Server and DNS server and send the result to me. 4. Please send these files with ISP DNS server's IP address. Besides, Id like to know if Exchange Server look for MX record from your internal DNS server and then DNS server forward the request to the ISP DNS server. Please post the Internal DNS Lookups settings and external DNS lookups settings. Regards, Xiu