I was shocked to learn about the restriction Ghost has on setting up bulk mail. After reading the four articles you linked, I think there are a few misconceptions on your part.
It seems like you are associating SMTP with self-hosted mail, and proprietary mail APIs with mail providers like Mailgun. This is not true. These APIs are simply an abstraction layer over regular SMTP, designed to make it easier for developers to send mail by not requiring an SMTP client. The use of SMTP does not indicate whether self-hosted mail is being used.
Individually trying to support every mail provider’s proprietary API neither practical nor necessary, as SMTP is the standard for sending mail, regardless of whether you are self-hosting mail or using a bulk mail provider. Applications like Discourse and WordPress just ask for SMTP credentials, like they should, they don’t individually support every bulk mail provider out there.
Therefore, please allow us to use SMTP for bulk mail. I would really love to use Ghost for my personal site, but I do not want to be restricted to using one of the few bulk mail providers supported.
No one is disputing that SMTP (a protocol) is used for sending high-volume email. But it is wrong to compare an SMTP server used to send occasional emails with one that is built to send in bulk.
Transactional email is sending to an individual for action, whereas marketing emails are messages sent to a bulk mailing list. Typically, a standard SMTP service can’t handle these lists because, for example, ISP SMTP servers have restrictions on volume or cannot be trusted to reliably deliver.
If you want to go down the SMTP route, you could use additional software like MailWizz. This behaves as an intermediary, and uses RSS and bespoke sign-up forms for campaigns (although it is typically used with APIs from Mailgun, Amazon SES etc.)
Alternatively, contribute to Ghost and add SMTP support so everyone benefits–but as I mentioned earlier, it’s not as simple as passing a large list to the SMTP server.
Please note, I’m a voluntary community moderator and not part of the Ghost team.
Nonetheless, if you wish to use SMTP for bulk email, you’re free to modify the Ghost code for this purpose. However, I and others don’t think this is the way forward. Providing additional bulk email API support via open-source contributions would be a better approach.