If somebody in the office tries to send an email to a particular domain eg DaveSmith@ValidDomain.com , then we get the following returned email: Your message did not reach some or all of the intended recipients. Subject: Test Email Sent: 30/03/2010 11:49 The following recipient(s) cannot be reached: DaveSmith@ValidDomain.com on 30/03/2010 11:49 You do not have permission to send to this recipient. For assistance, contact your system administrator. <MYDOMAIN #5.7.1 smtp;550 5.7.1 This system is configured to reject mail from XX.XXX.XX.X (DNS reverse lookup failed)> I have blocked out personal information but XX.XXX.XX.X is the external IP from our ISP to this office. If I try to email JaneSmith@ValidDomain.com we get the same undeliverable email. The annoying thing is that all other emails externally and internally are working. Is there anything I can try to troubleshoot this? I have already contacted our email host/provider and they have looked at their logs. They say the email isn't even getting to them. If this is the case, how on earth does my internal system just block this domain and no other?? Cheers, Ded You can't dangle the bogus carrot of possible reconciliation in front of me whilst riding some other donkey

On Tue, 30 Mar 2010 14:25:46 +0000, Ded_innit wrote:>>>If somebody in the office tries to send an email to a particular domain eg DaveSmith@ValidDomain.com , then we get the following returned email: Your message did not reach some or all of the intended recipients. >> Subject: Test Email > Sent: 30/03/2010 11:49 >>The following recipient(s) cannot be reached: >> DaveSmith@ValidDomain.com on 30/03/2010 11:49 > You do not have permission to send to this recipient. For assistance, contact your system administrator. > <MYDOMAIN #5.7.1 smtp;550 5.7.1 This system is configured to reject mail from XX.XXX.XX.X (DNS reverse lookup failed)> >>>I have blocked out personal information but XX.XXX.XX.X is the external IP from our ISP to this office. If I try to email JaneSmith@ValidDomain.com we get the same undeliverable email. The annoying thing is that all other emails externally and internally are working. Is there anything I can try to troubleshoot this?Is there a PTR record in DNS for the IP address XX.XX.XX.XX? If thereis, does the name match the data your server sends in the HELO or EHLOcommand?>I have already contacted our email host/provider and they have looked at their logs. They say the email isn't even getting to them. If this is the case, how on earth does my internal system just block this domain and no other?? What does your SMTP log file tell you about this? Is there aconnection to the ISP for ths e-mail? Or does the e-mail go directlyto the target domain?---Rich MatheisenMCSE+I, Exchange MVP--- Rich Matheisen MCSE+I, Exchange MVP

Hello, If your ISP is ATT, here's how to get a reverse DNS PTR: http://sharepoint.falconits.com/FAQ/E-Mail/ATT%20MIS%20Reverse%20DNS%20Pointer.aspx Also, chek out this on-line tool to check your PTR: http://www.mxtoolbox.com MiguelMiguel Fra / Falcon ITS Computer & Network Support, Miami, FL Visit our Knowledgebase Sharepoint Site

I am not an expert in Exchange by any means but can work my way around the system so bear with me if I don't understand something right away. You mention a PTR record in DNS but do you mean checking this on my Domain Controller. If so, no there isn't a PTR. If you mean something else, please could you describe exactly where I need to look. When you mention HELO and EHLO do you mean when checking the Logs (by default on my mail server in C:\WINDOWS\system32\LogFiles\SMTPSVC1). If I go to the day that my email was sent, I cannnot find the XX.XXX.XX.XX IP address that this undeliverable email returns. You can't dangle the bogus carrot of possible reconciliation in front of me whilst riding some other donkey

On Wed, 31 Mar 2010 10:40:30 +0000, Ded_innit wrote: [ snip ]>You mention a PTR record in DNS but do you mean checking this on my Domain Controller. If so, no there isn't a PTR. If you mean something else, please could you describe exactly where I need to look. Unless you own the network, or sub-network, the DNS PTR resourcerecord will be managed by your ISP. You should be able to use NSLOOKUPand do "set q=ptr" and then enter the IP address that the rest of theworld sees when it receives e-mail from your domain.>When you mention HELO and EHLO do you mean when checking the Logs (by default on my mail server in C:\WINDOWS\system32\LogFiles\SMTPSVC1). That's one way, but you'll only see the data portion of the HELO\EHLOcommand if you're collecting the right data. If you're not sure,modify the data your log file collects by checking every box.Another way is to watch port 25 with a network monitor (such asWireShark or NetMon) and see what your machine is sending.>If I go to the day that my email was sent, I cannnot find the XX.XXX.XX.XX IP address that this undeliverable email returns. That's not unusual. Most places run their LAN with a private IPnetwork (10.0.0.0/8, 192.168.0.0/16, etc.) and NAT the internaladdress. What the outside world sees is the NAT'd address.---Rich MatheisenMCSE+I, Exchange MVP--- Rich Matheisen MCSE+I, Exchange MVP