We are experiencing some issues receiving internet email on our Exchange servers. Just a little history of our network. We've had some DNS related issues over the last month or so, but we had someone from Microsoft correct them last week. Our Exchange configuration is as follows: 2 Exchange 2003 back end servers1 Exchange 2010 CAS/Hub/Mailbox (not internet facing) This has been in production for at least two weeks with no problems. We did add a DC to our AD domain on Saturday and I was told we were receiving internet email up until about 9:00am CDT today. I am seeing references to our non-existent domain that we removed about 3 months ago from our AD forest. Here is the error I'm seeing: (I don't recall seeing this before at least for several weeks) Event Type: ErrorEvent Source: MSExchangeALEvent Category: LDAP Operations Event ID: 8026Date: 4/5/2010Time: 10:50:05 AMUser: N/AComputer: EXMAIL1Description:LDAP Bind was unsuccessful on directory vpidc03.vintagerx.com for distinguished name ''. Directory returned error:[0x51] Server Down. DC=qualitestrx,DC=com For more information, click http://www.microsoft.com/contentredirect.asp. I'm also seeing this in our SMTP logs: 2010-04-05 16:39:51 62.134.45.37 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 451+4.1.8+Domain+of+sender+address+kbryant@qualitestrx.com+does+not+resolve 0 0 75 0 6796 SMTP - - - -2010-04-05 16:39:53 199.49.15.12 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 220+ap01.ey.com+ESMTP 0 0 21 0 6297 SMTP - - - -2010-04-05 16:39:53 199.49.15.12 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 HELO - outgoing.qualitestrx.com 0 0 4 0 6297 SMTP - - - -2010-04-05 16:39:53 199.49.15.12 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 250+ap01.ey.com 0 0 15 0 6609 SMTP - - - -2010-04-05 16:39:53 199.49.15.12 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 MAIL - FROM:<praimer@qualitestrx.com> 0 0 4 0 6609 SMTP - - - -2010-04-05 16:39:53 62.134.45.36 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 220+mailin5.rmx.de+ESMTP+RMX-Mail 0 0 33 0 2594 SMTP - - - -2010-04-05 16:39:53 62.134.45.36 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 HELO - outgoing.qualitestrx.com 0 0 4 0 2594 SMTP - - - -2010-04-05 16:39:53 62.134.45.36 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 250+mailin64.retarus.de+Hello+outgoing.qualitestrx.com+[74.51.106.99]+(may+be+forged),+pleased+to+meet+you 0 0 106 0 2875 SMTP - - - -2010-04-05 16:39:53 62.134.45.36 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 MAIL - FROM:<kbryant@qualitestrx.com> 0 0 4 0 2875 SMTP - - - -2010-04-05 16:39:58 62.134.45.36 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 451+4.1.8+Domain+of+sender+address+kbryant@qualitestrx.com+does+not+resolve 0 0 75 0 7156 SMTP - - - -2010-04-05 16:40:00 199.49.15.12 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 451+#4.1.8+Domain+of+sender+address+<praimer@qualitestrx.com>+does+not+resolve 0 0 78 0 12906 SMTP - - - -2010-04-05 16:40:01 199.49.55.212 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 220+em02.ey.com+ESMTP 0 0 21 0 891 SMTP - - - -2010-04-05 16:40:01 199.49.55.212 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 HELO - outgoing.qualitestrx.com 0 0 4 0 891 SMTP - - - -2010-04-05 16:40:01 199.49.55.212 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 250+em02.ey.com 0 0 15 0 1000 SMTP - - - -2010-04-05 16:40:01 199.49.55.212 OutboundConnectionCommand SMTPSVC1 EXMAIL1 - 25 MAIL - FROM:<praimer@qualitestrx.com> 0 0 4 0 1000 SMTP - - - -2010-04-05 16:40:02 199.49.55.212 OutboundConnectionResponse SMTPSVC1 EXMAIL1 - 25 - - 451+#4.1.8+Domain+of+sender+address+<praimer@qualitestrx.com>+does+not+resolve 0 0 78 0 1891 SMTP - - - - It is showing some 451's unable to resolve. While I was able to send successfully some test emails to my personal email account at Google, I do see some queues in a retry state on our SMTP connector. Nothing was changed on any of our Exchange servers and was working fine up until this morning. All internal email is still working. Please help as I have been working on this for the last few hours and have been unable to resolve. I've rebooted the servers, and restarted services but to no avail. Thank you, David Alge

This turned out to be an external DNS issue caused by our ISP who updated a SPF record incorrectly. Once they corrected the problem, emails are now arriving. Thanks!

This turned out to be an external DNS issue caused by our ISP who updated a SPF record incorrectly. Once they corrected the problem, emails are now arriving. Thanks! Thank you for your sharing! RichardYour expertise never fails to impress :)