A user object is created in the AD of the Client because they have existing portals referencing these objects for login details, we need a one-way sync to our Hosted Exchange environment where we then add the Exchange and Lync attributes. Passwords will always only be changed on the client's AD. (They actually have TDS syncing to a secure domain with FIM which in turn need to sync to us).

Then, if you only need those attributes, a set of scheduled tasks for export->transfer->Mangle if needed->import should work just fine.

I can set up scripts to do the exports and compare / imports. Do I need PES to export the passwords?

You stated in your comment that you only needed exchange and lync attributes. Using PES from ADMT for this seems like a bad idea; it's not what it was meant for.

I might have not come across correct, we need Name, Last Name, SamAccountName and Password to sync from the client. Sorry English is not my first language :)

So, if you're doing authentication, you should try ADFS. That's what it's for.

If I can convince them to use FIM is that the best option? Do we need a FIM installation on both our AD and the client's AD machines?

I don't believe FIM will sync passwords either

You only need one FIM installation to sync directories, it needs to be able to write to both of course.

Yup, though to. FIM can sync passwords when they're changed, but not any other time

technet.microsoft.com/en-us/library/jj590203(v=ws.10).aspx

End of my day, I have to go.

I appreciate your help! Thanks!

You got it