I get this guide is specifically about POP3 polling, but I think it should promote mail-receiver first instead of using a Gmail account, which should be the alternative, and not the other way as it is currently presented.
I’ve set up various Discourse installations and never went to mail-receiver, because I read “Gmail” first and thought “I know Gmail, let’s configure this” without actually trying to know more, or believing that the other way would be more complicated.
I finally tried mail-receiver and I think it’s just a better solution in all respects.
The Gmail solution requires configuring an app password in the Gmail account, which also requires two-factor authentication.
It’s a bit of a chore to do all of this, and in the end we get a reply-by-email feature with low polling rate (when mail-receiver is close to instant). It also relies on third-party software.
And I think another reason to promote mail-receiver is also that it doesn’t require more knowledge or technical skills than installing Discourse itself. It’s mostly a matter of DNS and yml configuration.
It is more technical than the Gmail solution for sure (though I’ve sometimes been lost trying to configure it, especially with app passwords), but if one has installed and configured self-hosted Discourse, then one can also install and configure mail-receiver.
And, perhaps more importantly and this is why I focus on this, the description of the Reply by email enabled setting links to this guide, not the mail-receiver guide:
Activate the feature that permits users to respond to topics directly through email, instead of requiring them to log into the website. See the guide on Meta for more information.