Ask HN: Why "do not reply" on rego emails

Why is it standard to have "do not reply" on registration emails (or any email from a company).

Couldn't you just add a "Reply-to"?

Wouldn't this be better?

I figure your customer has your email open at that point, they want to talk to you, they can just hit "reply" rather than going off to your website to find a contact form.. (like an idiot)

So any reason not to allow this?