I am trying to share (with full permissions) calendars across two different exchange servers in two locations. So here is the setup:

1 x Exchange 2007 (location 1)
1 x Exchange 2003 (location 2)
Different versions of Outlook (ie Outlook 2003/7)
Localised GAL for each server (so they are not shared). There is no VPN between the two servers but that can be setup. They are not part of the same domain, forest etc.

Basically I want to add/edit/delete events on some other users account in the exchange 2003 server from location 1.

I googled and found that there are a few ways this can be done but no definite solution. These include using webDAV (but I think this only work with outlook 2007) and merging the 2 exchange servers.

I am also a bit new at using Exchange, so I am still trying understand how the 'black box' actually works.

  • I'm interested in doing the same. We already have the trusts established where I am, but all we see is the free/busy info of the users on the other Exchange server. Is there way to see the full details of someone's calendar? – mrTomahawk Jun 9 '09 at 3:03
  • @mrTomahawk: You would have to be given permissions to their calendar on their domain - either by calendar sharing or through AD/Exchange mailbox permissions. With trust relationships, even Admins are just regular users on the other domain – Zypher Jun 10 '09 at 4:01

As mentioned by LEAT, to do this you will need to setup a trust between your two seperate Active Directory Forests. Firstly, you will need a link between the Forests, in your case it looks like your going for a VPN, once thats up you will need to setup your DNS on both domains so that the Exchange servers can resolve each other.

Once that is done you need to create the actual trust. There are two possible types of trust you can use here, an external trust, or a Forest trust.

  • An external trust is a trust between your Forest and a single external domain
  • A Forest trust is a trust between your forest and another whole forest, so you will trust all domains in that forest.

To set one of these options up, take a look at one of these articles:


First question are both exchange servers in the same domain/forect/organization? - if you open the Exchange system manager on one server, do you see both servers or not?

If yes, then actually it should just work, might need to add some permissions if you want to do more then just view.

If they are in different organizations (being exchange organizations that is) then it get complex. In a nutshell you need to setup a trust between the two domains, and both servers need to be able to resolve names from the other server.

Do you have a perm VPN link between the sites? Are both sites part of the same Windows Domain? Need more infomation before we can recommend anything.

  • I have updated the question to help answer some of your questions. Also how do you setup trust between the servers? – Harvy Jun 8 '09 at 11:45

As others have said, the first part is to establish a trust relationship between the two domains. Now the hard part comes in since you are in different forrests this gets to be quite the PITA. Although the one readeaming thing is one of the servers is Excahange 2007.

This blog post from the exchange team will help you out greatly:

You can read up on the IORepl pain that was exchange 2003 via the link in the post.


Well thanks for the great responses and I am sure these answers will be of great help to some people.

But basically, all I need was to share a few calendars between the two organisations. So we went via the third party HTTP option.

So I installed 'Google Cal Sync' on both machines and hooked it up to one Google account. So both Outlooks had access to a joint calendar, with the appropriate permissions. As setting all this up (and learning it) would take up time, that we just didn't have :-(

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