I suggest you try it. It has been tested with Gmail, but we haven't been able to test other providers there.
The switch offers no explanation and seems not to do anything.
The switch enables that configuration, but it only applies if an emailer plugin isn't activated.
OK, thanks for the explanation.
I think I will stick to the external SES plugin since, as far as I understand, this whole section is about using SMTP for sending e-mails which requires storing credentials in database. We use IAM roles to grant implicit permissions to use SES on instances that run our Forums - and nodebb-plugin-emailer-ses is able to pick that up.