I have seen this question being asked in the forum a couple of times and I thought it may be a good post to write. So, I decided to spend the next 30 minutes to blog about this.

Many of you here probably have some good experience with Exchange Server 2007 Address List Segregation. We have a white paper on how to configure this. It is here.

Those who has been managing Hosted Messaging and Collaboration (HMC) should also know  that Microsoft uses the similar concept to create address list segregation. Of course, in HMC, there are more such as inclusion of transport agent to deal with OOF or SMTP event sink and etc.

I also know that there are some hosters who have configured Exchange Server 2010 with the similar address list segregation concept and offer commercial Hosted Exchange even though it isn't supported by Microsoft.

Now, with Exchange Server 2010 Hosting Deployment being available officially now in SP1, I thought I should mention why you should really move towards that instead of staying with the legacy Address List Segregation method if you are a hoster,

• Support: Firstly, Address List Segregation Method isn't officially supported by Microsoft. Please see the current support stance from Dgoldman's MSDN blog, http://blogs.msdn.com/b/dgoldman/archive/2010/05/10/critical-update-exchange-2010-address-list-segregation-and-current-support-stances.aspx
• Level of Segregation: Address List Segregation, that alone should already tell you. This method focus primarily just on Address List segregation. Exchange Server 2010 SP1 Hosting Deployment introduces a whole new level of segregation, such as
  • OU segregation: Each Tenant Organization is located in its own configuration OU. That will give tons of flexibilities such as you can disable auto-forward by Tenant OU.
  • Mail delivery segregation is out of the box. In an address list segregation, you will need to create a transport agent to do the appropriate segregation, to avoid internal and external OOF being sent incorrectly.
  • Each Tenant Organization can have their own management role defined easily, such as you can specify whether they can manage distribution group or not just for that OU, very easily.
  • Each Tenant Organization can have their own organization transport rules.
  • Each Tenant Organization can have their own recipient enforcement provisioning policy such a limiting the number of users being created.
  • Each Tenant Organization will have their own accepted domain that they can manage but yet remain totally segregated from other organization.
  • Each Tenant Organization can have their own ActiveSync Organization settings, policy, device class settings and etc.
  • Each Tenant Organization can have their own CAS-Mailbox Plan and Mailbox Plan.
  • Each Tenant Organization can have their own Email Address Policy
  • Each Tenant Organization can have all their usual address lists, like all rooms, all users, all distribution groups and etc.
  • Each Tenant Organization can have their own Role Assignment Policy, OWA Mailbox Policy, Throttling policy, Retention Policy Managed Folder policy and etc.

What I mention above is by no mean the full list. But as you can see, Hosting Deployment can literally allow you to offer your customers a 'full' Exchange environment with all the policies that they can have but yet in a shared hosted environment.

Just based on above, I think there is no reason to consider Address List Segregation if you are a hoster for the next generation of hosted Exchange, right? :)