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Email not being sent by smarthost

I have an exchang 2003 server setup that has been running wihtout problems for a few years. Just this week, I changed the connector to forward mail to a smart host. This is a computer on my "optional" network as a Watchguard firewall would term it which has all ports opened between them on the firewall. Most email is being sent without problems, but I have a few that are either sitting in the queue on the smarthost (C:\Inetpub\mailroot\Queue). I have a user who got a NDR stating that his email was returned because "You do not have permission to send to this recipient".

I dont understand if that error message is coming from my side or theirs.

If I look in the event viewer on the smart host, I see a ton of smtpsvc notices that say: "Message delivery to the host 'x.x.x.x' failed while delivering to the remote domain 'x.com' for the following reason: The connection was dropped by the remote host."

What might cause this connection to be dropped?

I have run NSLOOKUP, SMTP DIAG, and checked to ensure I was setup for reverse dns. All came back saying all is OK. Both nslookup and smtp diag successfully translated the address and I am also able to
telnet to mail.domain.com 25

I dont understand enough about what may have happened while sending to the smarthost. Most email is being sent fine, but just a few are having problems.

Thanks.
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adembo
Asked:
adembo
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1 Solution
 
ademboAuthor Commented:
The smarthost is not a member of my domain. Reverse DNS is setup to resolve to the mail.domain.com as I have it, but that is then NAT'd to my mail server and not the smart host. Does that give problems being that the FQDN that is for my email domain is not the same as my smart host?
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ingeticCommented:
Is the smathost an ISP one, or a samrthost where you have full relay rights without detecting if it can be a spam or , ...
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ingeticCommented:
Why don't you use a smarthost if the smarthost is not in your domain instead of simply create a connector ?
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ademboAuthor Commented:
The smarthost is mine. I have it setup to allow relaying from my mailserver. (By IP)
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ademboAuthor Commented:
Not sure I understand you. I did create a connector on my mail server which is forwarding the mail to my smarthost (gateway server). This is done because of our GFI mailessentials software. It can scan the email before it reaches our mailserver. I dont want the smarthost to have rights onto our domain in case of virus outbreak.

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ingeticCommented:
ont the smarthost, do you have GFI mailessentials . mailsecurity . ??? .
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prashsaxCommented:
It could be due to some domains have installed antispam solutions.

And when your smarthost tries to send the mail on behalf of your domain, the antispam server will try and do a reverse lookup. Now the reverse lookup will resolves to some other IP address.(Other than your smarthost).

So the antispam server will drop the email as the mail server for your domain is not the one trying to send mail on your behalf.

To, solve this, create another MX record for your domain name and point to smarthost with some high preference number.(So that I should not be used).

With this, antispam server will not drop your mails.
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ademboAuthor Commented:
It looks like this was related to my reverse dns lookup. When I went to www.dnsstuff.com and did a query for it, it showed correctly. When I sent an email to my email account (on the internet) I noticed that it had the wrong IP address for it. This was caused by my Watchguard firewall which was labeling any outgoing traffic with the same IP. When I changed that, the email is not being received by the destination.

Thanks for help.
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ademboAuthor Commented:
I accepted prashax's response because he/she was on the right track.

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