To remove an Exchange user you need to do so in two different places:
Removing a User from the Spam Filter
Browse to Mailadmin.yourdomain.com and log in.
After you log in with the admin account you will see the following:
Click on the domain to view settings & users for the domain.
You will then see a list of all of your users that are being filter for spam.
To remove a user, find the one that you wish to remove.
Then click on the Action drop down list, and select delete user.
*You will want to be sure that you also remove that user from the Exchange side as well.*
Removing a User from the Exchange Server
Browse to OWAadmin.yourdomain.com and log in.
Once you log in you should see the following, click on “Hosted Organizations.”
Then click on the domain:
After clicking on the domain you will see the following, from here you can add/remove you user accounts.
Click on “Users.”
You will then see your user list.
If you wish to delete a user you can pull up your user list and click on the red “x.”