Exchange 2010 SP1 routing: auditing current mail routing

The get-adsitelink cmd-let allows you to view the cost metrics associated with AD sites in your organization. You can use this information to determine how mail is routed within your organization. Keep in mind that if you only a select number of internet facing hub transport servers all mail routing to the internet goes through them. Therefore, you must calculate the cost from any given hub transport server to these servers to determine which one will be used for internet bound email. Hub transport servers with a send connector namespace of * will be "catch-all" send connectors matching all destination email domain namespaces not specified by any other connector in the Exchange Organization.

http://technet.microsoft.com/en-us/library/bb123486.aspx

You could override the AD site cost to manipulate the way exchange routes using:

Set-ADSiteLink –Identity 'Atl-Nyc' –ExchangeCost 10

If you decide to remove this Exchange specific configuration for Site link Cost you can do so:

Set-ADSiteLink -Identitiy ' Atl-Nyc' -ExchangeCost $null

For a list of all of the "Sites" in active directory use get-adsite

http://technet.microsoft.com/en-us/library/bb124239.aspx

A bit simplistic, but viewing all of the hub transport servers in your Exchange organization is important be sure to use get-transportserver

http://technet.microsoft.com/en-us/library/bb125246.aspx