Exchange 2007 GALS between two domains

exchange-2007windows-server-2003windows-server-2008

Here's our Exchange 2007 Scenario. (2 Exchange Servers on a different forest)

For ABC.COM Exchange domain
250 mailbox users
300 mail contacts that we added to represent the other Exchange DEF.LOCAL domain users
60 Distribution groups

For DEF.LOCAL Exchange domain
200 mailbox users
350 mail contacts that we added to represent the other Exchange ABC.COM domain users
80 Distribution groups

The primary email address we are using that is configured in Exchange server is DEF.NET. Basically, for us ABC.COM users, we can send outgoing email and we can also receive incoming email as long as the email address is ABC.COM. But if someone wants to send an email to our DEF.NET email address, we need to ensure that the corresponding ABC.COM user mail contact is created in the DEF.LOCAL Exchange Server Mail Contacts section with an smtp address of user@DEF.NET.

In addition, in order for us to be able to send emails to users of DEF.LOCAL, we also need to ensure that their corresponding DEF.NET mail contact is created in the ABC.COM Exchange Server Mail Contacts section with an smtp address of user@DEF.net

This is also the same case of DEF.LOCAL Exchange users. Since their primary address is DEF.NET, they have no problem of sending and receiving emails from outside. But since the company requires us to use DEF.NET as the primary email address for both Exchange domains, in order for DEF.LOCAL users to be able to send emails to ABC.COM, the corresponding ABC.COM mail contact is created in the DEF.LOCAL Exchange Server Mail Contacts section with an smtp address of user@ABC.com.

By the way, both domains have domains trust in each other as well. The AD/DC OS on both forests are running Windows Server 2003 Standard. The version of the Exchange we have is Exchange 2007 SP3 installed on a Windows Server 2008 OS.

I am looking at GALsync program (http://www.msexchange.org/articles-tutorials/exchange-server-2003/migration-deployment/GAL-Sync-Identity-Integration-Feature-Pack-IIFP.html) but I am not sure if this will solve everything. Basically, since we're able to see users from the two Exchange domains with the use of Mail Contact, the objective now is for us to be able to see the corresponding distribution groups for both Exchange domain within Outlook GAL. As of now, the only way for us to be able to send email to the distribution group across the other Exchange domain is to create a corresponding mail contact of the particular distribution group. Although that works, it would sure be nice if we could also see the members of the distribution group as well from the other Exchange domain.

Thanks for taking the time to read this and thank you everyone in advance for the help and advice.

Best Answer

I have done a setup just like you are asking, albeit with Exchange 2010 which is somewhat different than 2007 in this regard. It will handle distro lists, etc. Be cautious about having the same ones cross-forest though...like helpdesk or sales or whatever.

Basically it comes down to 3 things:

  1. You should (if you don't already) have a shared SMTP namespace for DEF.NET. This will make sending and receiving as DEF.NET for EVERYONE...and simplify the namespaces used. You can do this cross-forest.
  2. Exchange 2010 simplifies this part, but it is still doable in Exchange 2007 with the latest SP I believe. Look into Cross-Forest Federation, if needed. Basically this will allow for cross-forest resource availability and free/busy sync. Helps for meetings, etc
  3. We used (and I highly recommend) a product by netsec.de called GAL Sync...http://www.netsec.de/en/produkte/galsync/ It is made by a German company but it has full english support and works amazingly well. It will require setting it up on both sides, but it works so well with so many customizable options. We had looked into all the others, like IIFP (now ILM), Quest Collaboration Services, doing it in house, manual contacts on both sides, etc.

This isn't for the faint of heart overall though. You have to really make sure you do it right, because Exchange is finicky. Take for instance a single contact you already have on the other forest. Now delete it and recreate it and watch what happens when someone tries to reply to an existing email from the original "contact". It will bounce because it is looking for that original Exchange object, not the smtp address. So be careful and go slow. Even with the above options, it took me a few months of planning and testing to make sure go live would go smoothly.

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