Unable to send mail - 4.2.1 Unable to connect error

Hi all,

I have a strange problem. everything has been working fine for a number of months then suddenly, no one could send email. recieving email is ok however.

details;
just the one server
Win server 2008
exchange 2007
symantec endpoint protection

the mail queue gives me the below error;
451 4.4.0 Primary Target IP Address responded with:"421 4.2.1 Unable to Connect"

which points me to a DNS error but nothing has changed, have flushed and registered which did not fix it. I did find that I can telnet to port 25 from external to the server but I cannot telnet from the server through port 25. I have tested telnetting to port 25 from a workstation in the same domain and is ok so it has to be the server. I have turned off the firewall and anti-virus just to test but still nothing. I can however telnet through other ports, just not 25.

any help would be appreciated.
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TimbobalobaAsked:
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TimbobalobaAuthor Commented:
Fixed. Turned out to be the router!!! was blocking port 25 from just the server. replaced the router and all working fine now!
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Glen KnightCommented:
OK, can you have a look at your Queues do they give an error message?

Turning off firewall and antivirus will not help it must be uninstalled to eliminate this as the problem.
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TimbobalobaAuthor Commented:
error;
451 4.4.0 Primary Target IP Address responded with:"421 4.2.1 Unable to Connect"
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Glen KnightCommented:
"Turning off firewall and antivirus will not help it must be uninstalled to eliminate this as the problem."
Please uninstall your virus software/firewall and restart the server.
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TimbobalobaAuthor Commented:
Anti-virus removed , server rebooted and still unable to send.....
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Glen KnightCommented:
Can you check the properties of your Send Connector under organisation Configuration > Hub Transport.
Are you sending via DNS or Smarthost?
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TimbobalobaAuthor Commented:
DNS
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Glen KnightCommented:
OK.
Can you check that you have a valid rDNS (PTR) record configured.
Also check you have an SPF record.  Goto http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/ and check.

There is also a good FAQ here from EE Expert alanhardisty that may help you identiy where the problem lies: http://www.it-eye.co.uk/faqs/readQuestion.php?qid=2
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TimbobalobaAuthor Commented:
rDNS is correct.
SPF record is good

I feel it has something to do with being unable to telnet from the the server. what would stop this?
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