Hi there, I have an issue on a client'sExchange server where they can't email one specific address. I can email the address from my Exchange Organisation, so I know the address is valid. However, they get the following: The following recipient(s) could not be reached: user@domain.co.uk on 22/03/2007 16:25 There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <mail.domain.co.uk #5.5.0 smtp;550 relay not permitted> They are running Windows 2003 SBS SP1, with Exchange SP2. I don't know what the remote system is running, but when I telnet to it it identifies itself as Microsoft ESMTP MAIL Service, Version: 6.0.3790.1830, so I think that means it's Exchange 2003, but I'm not sure if that enlightens me on the service pack level. They don't have this issue emailing other people, it is just one case where they have the problem. I'm stumped I'm afraid, I can't see what I'm missing. Their setup and ours are pretty much identical so I don't know why ours should work when theirs doesn't. Any advice or suggestions will be gratefully received.

It could be that the IP address your client's sending SMTP server has a missing or invalid PTR record. See the following article for further information. http://support.microsoft.com/kb/300171 Tony www.activedir.org

Hi Tony, Many thanks for responding. As it happens I have already looked into that possibility. I do tend to use dnsreport.com for this kind of issue to see whether I have something like that going on and I have certainly seen that before. I did notice that I had an issue where the mx record was 'mail.domain.com', but the server identified itself just as 'domain.com' in its header. I corrected that thinking that may be the issue if the other server was doing some sort of reverse lookup. However, that hasn't fixed it and myMX record is theA record 'mail.domain.com' whichis '1.2.3.4' and thePTR is '4.3.2.1.in-addr.arpa'. So far as I am aware, that is all as it should be although if I am wrong I'd be glad to know it. Out of interest there is no SPF record set up, but then there isn't one set up for the server which can email them successfully. Thanks again for responding. Any other thoughts? Cheers Neil