I'm just curious what the process is for setting up an email address policy for an exchange server that is running multiple different domains.I will be regularly creating new user mailboxes, some for domain A, some for domain B, others for domain C.

Email address is made up of local part, @ symbol, then SMTP domain name. Order can be important if you have many email address policies.

The default recipient policy creates two email addresses: a default SMTP address and an X.400 address.

Deleting email address rules in the default recipient policy: Rules in the default recipient policy can be modified to accomplish tasks like generating email addresses for an SMTP address space for your public/registered DNS domain.

They can be used to apply the policy irrespective of the recipient's location in the Active Directory hierarchy of containers and OUs.

If you need to apply the policy to all OU recipients, you can either use the common attributes or one of the extension attributes -- perhaps by populating one of them with the name or the distinguished Name of the OU, or some other string.