Creating a New User (Remote Mailbox)

Start in Exchange Recipient Configuration, under Mail Contact:

Create New Remote Mailbox:

Choose new User Mailbox, and click Next:

Next, you need to select the option to specify an OU, and click Browse:

Select the correct OU, and then click OK:

Fill in the rest of the user information making sure to select domain (or email address) as their UPN, and click Next:

Add an Archive Mailbox if required:

Check over the configuration summary, and then click Next:

Once the process completes, click Finish:
Go ahead and force sync