In co-existence scenarios, the targetAddress attribute is leveraged to accomplish routing to different Exchange organizations by specifying the “final destination” e-mail address. The e-mail domain part of this address can be a non-accepted domain (i.e. other organization). This will enable organizations, when used in conjunction with mail-enabled users or contacts, to provision the (global) address list of their Exchange organization with mail-enabled objects of other organizations, also in a migration co-existence phase. Simply said:

1. It can allow users in the local organization to select the object from the (global) address list and that object exists in other organizations;
2. Exchange can route the message to its final destination using the specified targetAddress.

Reason for this blog is that I still see people putting e-mail address in the targetAddress property or the object by scripting against Active Directory (e.g. ADSI), even while they’re scripting using the Exchange Management Shell.

In the Exchange Management Shell, you can set the targetAddress by using the Set-MailContact or Set-MailUser in conjunction with the ExternalEmailAddress parameter, e.g.:

Set-MailContact  michel -ExternalEmailAddress michel@contoso.com

Setting this address is also possible using the Exchange Management Console, which may be more appropriate for testing purposes or a small number of changes (though I’d prefer the less-prone-to-error script any day):

When utilized in scripts, you can use PowerShell Piping Power (is that abbreviation already taken?) to process (CSV) files or use filtering to select the objects of which you want to configure the targetAddress, e.g.:

Get-MailContact -OrganizationalUnit “contoso.local/Division” -Filter {EmailAddresses -like *@contoso.local} -ResultSize unlimited | ForEach { Set-MailContact –ExternalEmailAddress “$($_.Alias)@newcompany.local” }

Get-Content “users.txt” | Get-MailContact | ForEach{ Set-MailContact $_.Identity -ExternalEmailAddress “$($_.Alias)@newcompany.local”  }

This will configure all mail-enabled contacts in the Division OU with an @contoso.local e-mail address with a target address which consists of the current alias followed by @newcompany.local. The other example uses a text file with names to process contacts and set the targetAddress to the current value of “alias” followed by the external e-mail domain.

Needless to say, the connectors between contoso and newcompany  as well as the accepted domains should be properly configured to route those contoso.local and newcompany.local domains between those organizations. Of course, this also depends on whether you’re using internal or external domain names and if you want those messages to go through the public network or not.

Note that this is also how you can set configure the targetAddress of a local (DirSync’ed) mail-enabled contact with an Office 365 mailbox in a Hybrid setup, for example after moving the mailbox to Office 365. In such case you set the targetAddress to the service domain in a Hybrid Office 365 setup, e.g. mydomain.mail.onmicrosoft.com.