After upgrading our Hub and Edge servers to Exchange 2007 sp3, we have noticed an issue where emails to selected domains are no longer able to be sent. The errors for the 2 domains are 421 Service not available, closing transmission channel and attempting to send to yahoo.co.in 421 4.4.2 Connection dropped Before the upgrade we had a similar issue not being able to send to 1 or 2 domains, however this was fixed by adjusting our Internet edge connector to 'Use the External DNS lookup settings on the transport server'. Performing the telnet test to both of these domains fails. For example for yahoo.co.in - telnet mx1.mail.in.yahoo.com 25 220 mta1000.mail.in.yahoo.com ESMTP YSmtp service ready ehlo <insert our domain> 250-mta1000.mail.in.yahoo.com 250-8BITMIME 250-SIZE 41943040 250 PIPELINING mail from:test@domain_name 501 Syntax error in parameters or arguments The connection to the host is then lost. For the first domain (a customer so I won't reveal the domain name), after we telnet in we type 'ehlo <insert our domain>' and the response is 500 Command unrecognized "XXXX XXXXXXXXXXXXXX" Any ideas on what the cause may be? Trawling the internet hasn't helped me on this one. TIA Mic

On Wed, 3 Nov 2010 00:30:02 +0000, Mich2w wrote: > > >After upgrading our Hub and Edge servers to Exchange 2007 sp3, we have noticed an issue where emails to selected domains are no longer able to be sent. The errors for the 2 domains are > >421 Service not available, closing transmission channel > >and attempting to send to yahoo.co.in > >421 4.4.2 Connection dropped > >Before the upgrade we had a similar issue not being able to send to 1 or 2 domains, however this was fixed by adjusting our Internet edge connector to 'Use the External DNS lookup settings on the transport server'. > >Performing the telnet test to both of these domains fails. For example for yahoo.co.in - > >telnet mx1.mail.in.yahoo.com 25 220 mta1000.mail.in.yahoo.com ESMTP YSmtp service ready ehlo <insert our domain> 250-mta1000.mail.in.yahoo.com 250-8BITMIME 250-SIZE 41943040 250 PIPELINING mail from:test@domain_name 501 Syntax error in parameters or arguments Well, since the only command you sent was "EHLO <insert our domain>", you'd have to be sure that "<insert our domain>" was represented in your public DNS. Usually, the EHLO uses the FQDN not the domain, but if the domain is represented by an A (or CNAME) record in DNS it should be okay. >The connection to the host is then lost. >For the first domain (a customer so I won't reveal the domain name), after we telnet in we type 'ehlo <insert our domain>' and the response is 500 Command unrecognized "XXXX XXXXXXXXXXXXXX" > >Any ideas on what the cause may be? Trawling the internet hasn't helped me on this one. The response simply says that EHLO isn't acceptable. You should use HELO instead. From RFC2821: 3.2 Client Initiation .. .. .. .......................................For a particular connection attempt, if the server returns a "command not recognized" response to EHLO, the client SHOULD be able to fall back and send HELO. --- Rich Matheisen MCSE+I, Exchange MVP --- Rich Matheisen MCSE+I, Exchange MVP

Hi Rich, Thanks I did try helo as well, sorry I didn't mention that. I believe the issue is with reverse lookup failure for our outgoing mail servers. Our network team are looking into this at the moment. Will post an update when we have further information. Thanks for your help. Mic

If there is any update, please post it here to let us know. If the issue persists, I suggest you also temporarily disable your antivirus program and check the result. Thanks.Novak Wu-MSFT