Delivery failure when sending mail to specific domain with exchange 2003

Posted on 2004-08-12
Last Modified: 2012-06-27
I have a problem with sending mail to a specific external domain from exchange 2003. Mail sent to any address at that domain just sits in a queue until it eventually generates an NDR with status number 4.4.7.
The error message for the queue just says 'An SMTP protocol error occurred'
I found a couple of kb atticles relating to this error but they seem to be about open relays and I know the exchange box is not an open relay.
I can send mail to this domain from a hotmail account so I know the address is correct.
I'm new to exchange 2003 so I'm a bit stuck as to where to look.
Any suggestions?
Question by:howardphillis
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LVL 17

Expert Comment

ID: 11783305
can you trace a route to the domain... find out how many hops there are to it from your domain... if there are too many then we can up the hop count

can you telnet to the server in question... if you can then we can troubleshoot some more.;en-us;153119

my first guess would be the hop count as in this doc;EN-US;284204

Author Comment

ID: 11784148
OK, I can telnet to the server and get the following results:
If I try to send mail to either the domain in question or to a hotmail address then I get a 550 unable to relay error
I can send to an internal address without problems

I've checked the MX records for the domain in question and mail is handled by and
When I ran a traceroute to either of those servers fqdn or IP address using NetscanTools it failed. It also failed using the Mac OS X Network utility and a couple of online traceroute services.
What I dont understand is how I managed to send mail to that address from a hotmail account.
I could increase the max hop count to 30 but I can't really see it making a difference.
LVL 17

Expert Comment

ID: 11784226
sorry the hop count was from the line mixed up on the error message.

how about trying this ....setup a connector in Routing groups. you don't need to use the connector for all domains. If you drop the * and enter,, etc to the list  the connector will be used for just those domains.
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LVL 17

Expert Comment

ID: 11784248

Author Comment

ID: 11784453
RDNS sounds interesting. Just one question - is it a setting you can switch off in exch2003 or is it on our internal DNS server? We currently have no Reverse Lookup Zones configured so I'm not quite sure how I would switch it off.

As for the Routing groups suggestion I remember having some success when I had a similar problem in Exchange 5.5 so I'll give it a try and report back
LVL 17

Expert Comment

ID: 11784661
go to and do the reverse lookup test
You might also want to look at and see how your domain looks.

LVL 17

Expert Comment

ID: 11784843
if you have no PTR record then get your isp to set this up for you.

Author Comment

ID: 11785475
there is a ptr but it doesn't seem to be correct.

The MX record shows that mail for is handled by

If I do a Reverse DNS lookup for the IP of I get PTR record:

which seems wrong to me
LVL 17

Accepted Solution

Microtech earned 250 total points
ID: 11921633
you could try and set up a SMART host for this domain see how you go after that?

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