In doing some research into Hosted Exchange and the deployment of OWA, the question of how can OWA be customized

First, let's you should take a read into a Microsoft Support Article that discusses how OWA can be customized on a per user basis.  Below is the link:

http://support.microsoft.com/Default.aspx?id=833340

So basically, customizing OWA per user is all about providing a number (All be it a special number) on the "DefaultMailboxFolderSet" on the User Object in Active Directory.  Now you can either do this via a script of using ADSI Edit (a utility that is available when you install the Windows 2003 Support Tools found in the Support folder of the Windows 2003 CD).

Now if you're doing this in a Hosted Exchange environment, the other mechanism to do this is via a "Plan" definition.  Plans in Hosted Exchange isn't really a fully featured Plan Management System, but it does provide a useful way to define user mailbox customization by defining it once and then calling the customization information by name per user creation.

At this point, I'm not going to discuss how Plans work and how to define new plans.  This is documented in the Solution Documentation, but I'll give my own perspective in a later post.

With that said, one of the "Sample" Plans that ships with the solution is named, "BaseMail" (this plan is created when you submit the request "CreateSampleServicePlans.xml" is submitted.  This can be found in the "C:\Program Files\Microsoft Hosting\Provisioning\HostedExchange\XML Initionalization\
" folder.).  This plan provides the consuming users of this plan to have the following features:

• Outlook Web Access (OWA)
• POP3
• IMAP
• Mailbox Size: 10 MB
• OWA Segment: 98821
• NoOutlookClient - This means that RPC over HTTP support for Outlook 2003 will not be available for this user.

The OWA Segment tag is actually a mapping to the DefaultMailboxFolderSet value stored in Active Directory for a user that has this plan.

So what does this standard user get with a number of 98821?

• Messaging (1)
• Contacts (4)
• Rich Client (512)
• Themes (32768)
• Junk e-mail (65536)

So this gives us a total number of 98821.  All of this is further documented in the solution documentation (Vol 3, Book 5, Ch 1, Service Plans & Events, Sample Exchange Mailbox Service Plans).