The “Manual polling enabled” setting is also found under Admin → All site settings → Email.
And since I apparently can’t sleep, I did some digging around and saw precious few cases of people trying to configure email-in via API. In case it’s any use to you as you proceed, here’s what I found:
(bunch of links)
As I searched, Discobot surfaced this perhaps outdated info:
You can use the Discourse API to handle incoming emails without relying on the mail-receiver container. The
/admin/email/handle_mailendpoint accepts raw email content via POST, allowing you to push emails directly to Discourse using a script or custom integration. This method bypasses the need for SMTP polling or the mail-receiver container entirely.For example, you can send an email to Discourse using a curl command with the
Learn more about the API endpoint in the Discourse API documentation.
(…I found nothing about it in the API documentation.)
2018: This topic didn’t seem to have a resolution.
2018: This post refers to an email guide – referencing language that no longer exists there – and also recommends: “Easiest way to get reply by email working is to use the mail-receiver container template, rather than trying to work with all sorts of varying APIs from the different providers.”
2022: The email parameter was to be changed to email_encoded.
2022: Another recommendation to just use mail-reciever.