Controlling outbound mail flow by server

We are new to this client and the previous provider set up three exchange servers for different purposes.    2 for delivery of bulk mail (they send subscribed advertising) and one more for the internal users.   Each is a mailbox server and a hub transport server.   They are each NAT'd to their own external IP in order to protect the users' server from the blocks that happen on the bulk servers.    
The problem is that the outbound delivery does not work like that and all hub servers are automatically distributed and users email is being sent by the bulk servers (and then getting blocked).  
What is the best way to fix this without adding additional servers as edge servers?  Is there a way?

Thanks in advance
~Jon
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Jon SnydermanAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
The simple answer is no. Exchange is designed to work together with other Exchange servers that are within the same domain.

So if you do not want Exchange servers to not communicate this way they need to be in a separate network/domain.

Will.
Jon SnydermanAuthor Commented:
Thanks Will.   Follow up idea.   If I break the business location in to multiple AD sites and then put the bulk mailers in that new site, would that keep the user server from utilizing the bulk mailer's hub server role?

I realized after posting that even adding edge servers would not help because I still cant depend on which hub it comes from, right?

Thanks!
Will SzymkowskiSenior Solution ArchitectCommented:
If I break the business location in to multiple AD sites and then put the bulk mailers in that new site, would that keep the user server from utilizing the bulk mailer's hub server role?

Even if you were to do this there is still a possibility that it could route through these HT servers. This would also be true if you only had 1 internet facing site in your Exchange environment.

If these servers need to be completely isolated create a forest root domain and spin up new exchange servers in there. For the purpose of isolating your HT traffic.

Will.
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Jeff GloverSr. Systems AdministratorCommented:
What version of Exchange are you running?
Jon SnydermanAuthor Commented:
They are running 2007 right now, VERY long story, but they were on 2000, now 2007, soon migrating to 2013+
Guy LidbetterCommented:
Hi Jon,

In certain circumstances there are things you can do. for example...

If you have the two bulk email servers in a separate AD Site as the users server, and configure separate send connectors for each site, this SHOULD effectively resolve your issue.

To break it down:

ServerA (User Mailboxes) in Site 1. Configure a Send Connector called "Users Mail" and scope the source server as ServerA's IP address.

ServerB and ServerC (Bulk Mailers) in Site 2. Configure a Send connector called "Bulk Mail" and scope the source servers with the bulk mail server IP's.

In Exchange 2007, when a mail is submitted to the submission queue, exchange will try load balance with any HUB servers in the same site. By segregating the sites you can potentially avoid this.

However, from exchange 2010, this becomes more difficult. As they introduced shadow redundancy, exchange will always try sending out of another Hub server so there are duplicate copies of a mail during transport. So an additional server in the user site would be a recommendation going forward. Since EX2010 uses site costing, it should always only go to the new local hub server.

However, in saying this, there is always the potential of mail routing through the alternate site, but this would only really be in the case of service failure.

Regards

Guy

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Jon SnydermanAuthor Commented:
Thanks Guy.   This helps a lot and was sort of what we were seeing.   The customer sends 50K+ emails a day and is concerned that the volume may trigger a failover to another site also.   Please with going toward 2013, your other point becomes an even bigger problem.

I think that we are going to rebuild one exchange server as a redundant server to the user server and put the undeliverables mailbox there.   Then take the third server and rebuild it with a software package specifically geared towards accomplishing this goal.   I think that may be a better use of resources.
Jon SnydermanAuthor Commented:
Unless there are any other ideas, thanks for everyone's input.
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