@atrilahiji You can use Ghost to do that, with the recent subscriber features.

I'd never heard of this before (never really used Ghost) and so I did a quick search and the top result says:

Subscribers was an experimental feature in Ghost, which has now been deprecated.

But it looks like it's been replaced with Members (beta) which looks like pretty much the same thing!

https://ghost.org/docs/members/requirements/

But, from the same like, it seemingly requires you use Mailgun

if you're self-hosting, you'll need to setup a Mailgun account in order to use the email newsletter feature in Ghost to send bulk mail. Read more about why this is required.

If you click the link it explains:

Why can't I just use SMTP mail config to send email newsletters with Ghost?

Sending a bulk email to many recipients using basic SMTP will result in your IP address being instantly blacklisted and marked as spam by all mail providers. You should never, ever send bulk mail using basic SMTP, which is why Ghost does not support it.

More info here, and here, and here, and here.

So I'm now also wondering if using MailTrain and/ or Mautic on Cloudron to send newsletters would also result in IP addresses being automatically blocked?!?

EDIT: ah, but also, seems could potentially use the Ghost Members feature but then send newsletters some other way (although maybe Mailgun is actually the best way to do it?)

I still want to use a different provider to send email newsletters, why can't I do that?

You can. There is no requirement to use Ghost's built in newsletter delivery feature. Before we released this feature in beta, thousands of people sent their newsletter using all sorts of other services such as Mailchimp, Sendgrid, Convertkit, and many others. You can easily sync your members database to an external newsletter provider via Zapier, or by following our detailed integration guides.

Maybe I'll try my hand at packaging a Golang app?

I jumped the gun a bit. Whoops... looks like its relatively unmaintained. Time to keep looking. I'd be very interested in something like this know so definitely let me know if you find a good one.