"this post arrived by email"

I’ve seen this on quite a few posts now, and I don’t really understand. How are people posting to a message board by email and why?

Go to your profile >> preference >> email and enable email notifications. That should let you post replies by email.

Kind of a funny sentence since ‘post’ can also mean a physical letter.

To possibly clarify a bit more: Discourse is set up where you can reply to an email notification, and it will show up as a new post.

Which seems like a neat feature, until you realize that by using it, you’re ignoring all of the other posts in the thread, so you might be repeating points already made by other posters in the thread, or dragging it back to a topic it’s moved on from.