I was recently contacted by a client inquiring how to forward a user's mail using MPS. There is no specific "provider method" for this, but it is actually very easy using the Manged Active Directory::ModifyUser method.
To enable forwarding, there are really only two properties that we need to be concerned about: altRecipient and deliverAndRedirect. altRecipient should be set to the DN of a mail-enabled object within the directory and deliverAndRedirect is a boolean that should be set to indicate if the mail should be delivered to the local mailbox as well as being forwarded or just to simply forward the mail.
The executeData blob of the ModifyUser method should look something like the following:
<value xmlns:dt='urn:schemas-microsoft-com:datatypes' dt:dt='boolean'/>
The tags have been discussed previously with the exception of the <user/> tag which should contain the LDAP path to the user object to be modified.