It’s easier/quicker to use the registar to configure the email provider but it still works with DigitalOcean if this provider is a pain in the ass to use. I should add a little disclaimer to this howto
The worst that I encounter was internet.bs, they sell domain name but if you don’t use their servers, you can’t configure anything (txt, cname) other than the dns domains. I had to use Cloudflare to link mailgun to the domain. It was fun.