Use any email address for approvers

Hi,

My organization is looking to utilize the approval feature more heavily going forward. Does anyone know if someone needs to be a service agent user to be listed as an approver?

I've tried to enter the email address of someone to be an approver in an approval process step and SWSD wouldn't accept the email address.

I believe that we have some approvers set up already who aren't service agent users, who also didn't show up when I typed their name into the approval process assignment box, but I don't know if I'm missing something.