There is absolutely no reason to only support Mailgun

[mjw]

See this thread:

Mailgun Alternatives

Why can’t bulks emails be a self-selected provider the same way that transactional emails are? You already posted the link the contains the overview of how the architecture works. So the broader answer is that you can’t send newsletters with SMTP, and while it is trivial to support multiple SMTP providers, it is not at all trivial to support multiple bulk mail APIs. A self-hosted ghost installation now costs you $35/month if you want to send bulk emails, on top of hosting costs [for ~100 em…