When you receive an email notification of a reply from the forum, please do not directly respond to the email. If you do, the person and forum will never see it. Instead, it lands in the forum email box, sits there, and rots away.
Instead, at the bottom of the email you received from the forum, click the “Visit Topic” to respond link. You’ll be taken to the forum where you can leave your reply.
Here’s an example of what it looks like.