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Unable to send smtp mail to one recipient

Posted on 2008-10-15
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Last Modified: 2013-11-30
I have a number of sites that I support all of which have SBS2003. In my own office I also run SBS2003 everything was fine until my own server crashed, I bought a new server and loaded it with SBS2003 R2 since then most of my supported sites work fine with mail being sent to me no problem, however I have 2 sites that can no longer send mail to me. They can however send mail to any other recipient via smtp. I have tried to telnet to my server via port 25 but cannot connect although they can connect to other mail servers.
I am banging my head on a brick wall now and cannot see where the break in communication lies, any help would be appreciated.
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Question by:jgharrison
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by:sstone55423
ID: 22720149
If you cannot connect to your server on port 25, you may have the Windows Firewall turned on.  As sending to those people worked before, perhaps hwne you set it up again after the crash you set it to require reverse lookup, and those domains don't have a proper PTR record?  Check to see, and if necessary turn off "perform reverse DNS lookup".  This should be in the properties of the SMTP virtual server on the delivery tab.  Also, you can turn logging on (on the general tab) and then check the logs after the other domains have tried to send to you.
 
 
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by:jgharrison
ID: 22721869
Thankyou for the reply,

I have checked the above and it seems the failures are not giving anything up in the log file other entries are coming in fine. To test things further I am sending no problem from the servers in question to other sbs servers I support so the only issue does seem to be at my end and there is nothing obvious that is happening only that the 2 servers in question do not seem to be getting a response from mine, so is there any way that my server is blocking only the 2 in question??

Regards

John
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by:sstone55423
ID: 22722897
Yes, if your server is doing reverse lookups, and they do not have a PTR record, you would get the symptoms you describe.  Turn off reverse lookups.  If they are already off, then it is likely a different issue.  If you do not see the other servers connecting in the log file and then some error mesage generated, then your server refusing connection because of reverse lookup failure could be the issue.
 
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by:jgharrison
ID: 22729278
Reverse lookups is not checked, so I guess that is not the problem, I try to connect using Telnet on port 25 and again I cannot get a connection, so somewhere there seems to be a break in communication.
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by:sstone55423
ID: 22736237
Checl to be sure that the windows firewall is turned off and then try telnet again.  Do you mind giving the email domain name?
 
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by:jgharrison
ID: 22736629
My email domain is smbnet.com or smbnetworksolutions.co.uk, the email domains that cannot send to me are porschebournemouth.co.uk, kw-eng.co.uk, and bournemouth-kawasaki.co.uk porsche can telnet to me on port 25 so can Kawasaki  and KW can as well now it seems they just do not connect to my exchange server.

Regards

John
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by:sstone55423
ID: 22737529
I ran diagnostics on all three domains, and reverse lookup succeeded on porschebournemouth.co.uk, and failed on the other three.
I can also telnet on port 25 to all of them.  I sent a couple of emails with the from domains porschebournemouth.co.uk and kw-eng.co.uk and the mail server accepted them without a problem.  I test sending to another domain and it rejected relay as it should.
If you can't telnet to port 25 on your server, we should try from various other places to isolate where it works from, and where it does not.
 
 
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by:jgharrison
ID: 22738784
I have managed a workaround on this problem, although it does not seem that my server is rejecting the mail due to Reverse DNS, I created a new connector and routed the mail via my ISP and the problem is resolved. Would like to find out however whether it was my server rejecting the mail or my ISP, I am guessing my server but cannot find out why, I was able to telnet to port 25 from all of the servers last night. Is there some way that the servers in question have lost the connection to my server due to it being down for a day or so? and for some reason holding some stale records or something?
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sstone55423 earned 500 total points
ID: 22744353
No, if you could telnet on port 25, then they wuold have been able to talk to it.  A liong shot is if you had changed the MX record recently, and the TTL time was high, like 24 or 48 hours, they would have held onto your OLD MX record until that cache time expired.  Since I was able to conenct and spoof email from their domains, your server was not rejecting them.  
Another long shot, since several of them were on the same subnet, if you ahd the subnet mask misconfigured, that could cause an issue with them connecting.
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