Best Solution for handling multiple domains in Exchange

Posted on 2011-10-06
Last Modified: 2012-05-12
Hi Experts,
My client has a number of companies under a company group name.  Each company has its own domain name. We want to manage mail and share calendars across the group - also share files.  Can anyone suggest an Exchange solution for this?

Thank you  

Question by:freshfordian
    LVL 17

    Accepted Solution

    Actually Exchange 2010 out of the box will support this.  You can only have 1 organization per forest, so when you add exchange servers in each domain, they will automatically have the ability to share calendars across the group.

    Sharing files will be done via the trusts which are in place which are automatically created, however, you may want to create shortcut trusts to help improve authentication and access performance.  You will have to set up a careful model for permissions when you wish to share it with trusted domains.  You will have to make use of Domain Local groups with nested Universal Groups.
    LVL 1

    Author Comment

    Thank you LesterClayton for your comment
    When you said ..."you add exchange servers in each domain", we only have one exchange server!  While one company is quite large, the others are quite small (2-3users).. It would not be viable to provide these organisations with their own server.  Presently, each company uses POP3. Files are shred using DropBox.  Files on the the local server in the larger company are accessible using VPN connection to it.  I was considering a number of options that may or may not be runner
    Option 1
    Create an AD structure with the root of the AD as the group i.e., setting up subdomains for each company i.e. and assigning users, computers etc to each subdomain.  Then point for example at  That way mail addressed to would be aforwarded to At least, that's the theory!  I felt that this would also create a single logon solution.
    Option 2
    Hosted cloud solution.

    What do you think?
    LVL 1

    Author Closing Comment

    Greater clarification needed. My comment unanswered
    LVL 17

    Expert Comment

    I'm sorry I didn't provide a response to your additional comment. For an unknown reason, I wasn't notified of the response that you made.  Your query has however made me change my answer a little, and since you've awarded me points, it's only fair to respond.  One thing that confused me was the use of the word "Domain" - because you can have DNS Domain as well as Active Directory Domain.  I assumed Active Directory Domain because of the Exchange part.

    It's absolutely fine to have one exchange environment which hosts multiple domains.  All you have to do is add each domain as an accepted domain in the Hub Transport of the Organization.  (Organization Configuration - Hub Transport - Accepted Domains - add each one there.

    Your AD Structure you've suggested is fine - one Organizational Unit per "domain".  Option 1 is best for you.

    Option 2 is also possible, and ironically, something that I do.  I'm not permitted to advertise here though, so I cannot tell you more about it.  If you were thinking about installing your own exchange server in hosted mode - you cannot "legally" do this without having Service Provider License Agreement (SPLA).  You will not get support from Microsoft if you install your exchange in hosted mode and you do not own an SLPA.

    Once again, sorry about the miscommunication :)

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