I would like for approvers to be able to reply to an email with their approval decision - "approved" or "declined" and the request would be transitioned accordingly. This saves the user from the step of needing to login to approve/decline. 

Many of the approvers do not live in Jira and would have a more favorable experience with JSD if they weren't required to login to approve. It seems like an incoming email from the email address of the approver would be sufficient for verifying that the approval came from the denoted approver on the request.