I am Having a problem sending email to a particular domain. let us call it problemdomain.ie for the purpose of the discussion. I can send and recieve from other domains just fine. I am using SBS 2008 with Exchange 2007 I am using DNS for Delivery , and i also have checked the box in the Network Tab on the Send Contector Network tab to use external DNS Lookup settings on the transport server , and i have configured the Hub Transports esternal DNS Server to point at my ISP's DNS servers. When i open Nslookup ffrom the command line i get C:\Windows\system32>nslookup Default Server: UnKnown Address: fe80::1d11:6c69:c59:9c72 so i tell it to use the IP address > server 10.202.2.220 Default Server: [10.202.2.220] Address: 10.202.2.220 > eauctions.ie Server: [10.202.2.220] Address: 10.202.2.220 Non-authoritative answer: Name: problemdomain.ie Address: XX.XXX.XXX.XX <-- the correct IP and it resolves just fine. When I check the connectivity log i see the following CC9CC817F1FDB6,SMTP,problemdomain.ie,+,97d0d5db-0bc1-426d-b9e4-347c59db8bbe 2010-03-29T12:00:35.914Z,08CC9CC817F1FDB6,SMTP,eauctions.ie,>,DNS server returned ErrorRetry reported by 85.91.1.129 2010-03-29T12:00:35.914Z,08CC9CC817F1FDB6,SMTP,problemdomain.ie,-,The DNS query for 'DnsConnectorDelivery':'problemdomain.ie':'97d0d5db-0bc1-426d-b9e4-347c59db8bbe' failed with error: ErrorRetry I can see then that the SMTP Sen Conector is using the External DNS server but is failing to resolve from the Sever. When i then set this server in nslookup at the command line i get the following C:\Windows\system32>nslookup Default Server: UnKnown Address: fe80::1d11:6c69:c59:9c72 > server 85.91.1.129 Default Server: [85.91.1.129] Address: 85.91.1.129 > set q=mx > problemdomain.ie Server: [85.91.1.129] Address: 85.91.1.129 Non-authoritative answer: problemdomain.ie MX preference = 10, mail exchanger = smtpxx.cp.irishdomains.co m problemdomain.ie nameserver = ns1.irishdomains.com problemdomain.ie nameserver = ns2.irishdomains.com smtpxx.cp.irishdomains.com internet address = XX.XXX.XXX.XX ns1.irishdomains.com internet address = XX.XXX.XXX.XX ns2.irishdomains.com internet address = XX.XXX.XXX.XX > So I seem to be fine from the Command Line version of NS lookup but not from the one used in Exchange Anyone any ideas ? Best Regards Albert

FIXED ! I don't know what has fixed it but i think it was a problem with DNS I found that the ip address of the mail server that was stored in my DNS Cache was wrong. Even though I though I had switched on External DNS lookup somehow it got switchd off again . I foud this post which advised me to clear my cache on the dns sever http://blog.brainlitter.com/archive/2009/06/19/exchange-2007-difficulties-delivering-email-to-some-domains-%E2%80%93-error-451-4-4-0-dns-query-failed.aspx and then I checked the Smtp Send Connector setting and found the external DNS unchecked , once I ticked it again the message got delivered, 2010-03-29T14:13:16.269Z,08CC9D5838032365,SMTP,problemdomain.ie,+,97d0d5db-0bc1-426d-b9e4-347c59db8bbe 2010-03-29T14:13:22.347Z,08CC9D5838032365,SMTP,problemdomain.ie,>,DNS server returned ErrorRetry reported by 85.91.1.129 2010-03-29T14:13:22.347Z,08CC9D5838032365,SMTP,problemdomain.ie,-,The DNS query for 'DnsConnectorDelivery':'eauctions.ie':'97d0d5db-0bc1-426d-b9e4-347c59db8bbe' failed with error: ErrorRetry 2010-03-29T14:13:22.360Z,,MAPI,icmserver3.icm.local,+, 2010-03-29T14:13:22.388Z,,MAPI,icmserver3.icm.local,-,Messages: 1 Bytes: 4287 2010-03-29T14:14:08.263Z,08CC9D5838032366,SMTP,problemdomain.ie,+,97d0d5db-0bc1-426d-b9e4-347c59db8bbe 2010-03-29T14:14:14.065Z,08CC9D5838032366,SMTP,problemdomain.ie,>,smtp127s.cp.irishdomains.com[79.170.244.20] 2010-03-29T14:14:14.098Z,08CC9D5838032366,SMTP,problemdomain.ie,>,Established connection to 79.170.244.20 2010-03-29T14:14:14.497Z,08CC9D5838032366,SMTP,problemdomain.ie,-,Messages: 1 Bytes: 15506

can somebody tellme what was under that link? http://blog.brainlitter.com/archive/2009/06/19/exchange-2007-difficulties-delivering-email-to-some-domains-%E2%80%93-error-451-4-4-0-dns-query-failed.aspx thank you.