Prerequisites

In order to allow Approve/Reject via email you need:

The email's subject follows the convention below: Outgoing Email prefix - Project name / (Issue Key) Issue Summary / Source Workflow Status - Approval Required for 'Workflow Transition'.

Approve/Reject via e-mail

The approver can APPROVE/REJECT just replying to the received email by adding the following tags:

Moreover what you add after the previous tag is considered as an approval/rejection comment.

It's required that you always apply the tag @ to end your reply.