We recommend that each Active Directory site in a region that has one or more Internet-facing Client Access servers have a unique namespace. This is usually represented in DNS by an A record, for example, mail.contoso.com or mail.europe.contoso.com.
Exchange 2010 Organizational Models - Consolidated Datacenter Model This model consists of a single physical site. All servers are located within the site, and there's a single namespace, for example, mail.contoso.com.
- Single Namespace with Proxy Sites This model consists of multiple physical sites. Only one site contains an Internet-facing Client Access server. The other sites aren't exposed to the Internet. There's only one namespace for the sites in this model, for example, mail.contoso.com.
- Single Namespace and Multiple Sites This model consists of multiple physical sites. Each site can have an Internet-facing Client Access server. Or, there may be only a single site that contains Internet-facing Client Access servers. There's only one namespace for the sites in this model, for example, mail.contoso.com.
- Regional Namespaces This model consists of multiple physical sites and multiple namespaces. For example, a site that's located in New York City would have the namespace mail.usa.contoso.com, a site that's located in Toronto would have the namespace mail.canada.contoso.com, and a site that's located in London would have the namespace mail.europe.contoso.com.
- Multiple Forests This model consists of multiple forests that have multiple namespaces. An organization that uses this model could be made up of two partner companies, for example, Contoso and ContosoOnline. Namespaces might include mail.usa.contoso.com, mail.europe.contoso.com, mail.asia.contosoonline.com, and mail.europe.contosoonline.com.
 Important: |
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| We don't recommend deploying a topology that has a single namespace and multiple Active Directory sites. If your topology uses multiple Active Directory sites, consider using a regional namespace model. |
