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SMTP With Multiple Servers

Posted on 2006-06-27
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Last Modified: 2010-03-06
I've sucessfully installed my first Exchange 2003 server into my domain along with an existing Exchange 200 Server. Over the course of a few weeks, I plan on gradually moving the databases over to the new server and removing the Exchange 2000 server. My question is concerning outgoing SMTP.

If the given mailbox has been moved to the new server, obviously it will use the new server for outgoing SMTP, this works perfectly fine, but I'm wondering if this is going to cause problems with a lot of spam filters and such.

The MX record for the domain is set to the Exchange 2000 Server for now
Exchange 2000 server obviously also has an A record
New server does not have any external DNS records as of now
Both Servers have SMTP configured to announce themselves externally as mail.domain.com

If the mail is sent from the new server, obviously it has a different IP address than the Exchange 2000 server. If the remote mailserver does a reverse lookup on the ip, it won't resolve, but also won't match the ip address that it is announcing itself as. I can see this as causing a problem, any insight?

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Question by:jschweg
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Sembee earned 500 total points
ID: 16995531
Are you natting the IP address? You could NAT the two servers on the same IP. Then they would appear to come from the same address.

Another thing you could so is create an SMTP Connector. Set it to use DNS. Then set only the default SMTP VS that you want the email to leave the site using. The SMTP Connector can be set so that all other servers in that routing group will send email through that SMTP server.

Simon.
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by:jschweg
ID: 16996012
I don't have any NAT in my environment, we have a Class C at our disposal so we use a transparent firewall.

When mailservers preform a reverse lookup against the source ip, do they just verify that it resolves to something, or rather that it resolves to what you have configured as the FQDN under the SMTP Virtual Server?
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by:Sembee
ID: 16996198
Depends on how picky they are being.

Some sites will just want to know that it resolves - that there is a reverse DNS of some kind.

Other sites will confirm that the name in the SMTP banner matches the reverse DNS - ie you are who the DNS says you are.

You might get away with putting the same reverse DNS on to both IP addresses. I have one site with a dozen IPs and all of them have reverse DNS of office.domain.com

Simon.
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by:jschweg
ID: 16996491
Theoretically, couldn't I do this:

Rather than having both servers configured to use mail.domain.com as the FDQN, configure the SMTP FQDN on the new Exchange 2003 Server to "exchange.domain.com" and add PTR records to my external DNS so exchange.domain.com will resolve to the proper ip so nothing looks fishy.

Essentially both servers will announce themselves as two different machines when sending mail, but whenever mail comes back in, it will just obviously follow the MX record to the Exchange 2000 Server until I switch anything over.

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by:Sembee
ID: 16996524
You can do that if you wish.
I have multiple server sites where it is mail.domain.com, mail2.domain.com and mail3.domain.com
Although in those sites I am now using an SMTP Connector to route email out through a single server.

Simon.
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by:jschweg
ID: 16996631
I'm inclined to agree with the connector solution. Just seems like it would be a better, more consistent way to do this.

After going to <Administrative Groups -> Routing Group -> Connectors> and creating a new SMTP connector, I'm assuming that I just configure the other server to be a bridgehead and thats it?
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by:Sembee
ID: 16996732
SMTP Connectors are either Exchange org wide or Routing group wide.
Therefore configure the SMTP Connector and put the server that you want email to go out through as the bridgehead. When you ready to swap them over, simply change the bridgehead.

Simon.
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