We have an opportunity approval process that I created in our Sandbox. This process allows the submitter to manually choose the approver of the opportunity. As a part of that process I was able to create an e-mail alert that is sent to the approver by selecting the recipient "Related User: Approver" from the list of available recipients under the "Related User" recipient type.
I've recreated this approval process in our production environment and the "Related User: Approver" recipient is not available (I can only see the "Related User: Last Modified By" recipient option).
Anyone have any idea why the approver is not available for selection?
Here is a picture of an e-mail alert in our sandbox:
Here is a picture of an e-mail alert in our production environment: