I have been running my own services for years, all self-hosted, with different VPS providers: A2Hosting, Digial Ocean and now Contabo. I use ISPConfig and host about 25 domains and 200 email addresses. You have to configure SPF, DKIM, DMARC, reverse PTR address, but nothing impossible. Encountered some problems with some providers blocking the IP range of my VPS provider (Microsoft in particular), but if you send an email and explain you have a new server configured form scratch and carefully configured, they add an exception for your IP. Check your IP addresses are not list in any black list and you are done. I use Rspamd and I had to add some domains to the whitelist ... There are many servers out there (even of medium sized companies, very badly configured) that don't even respect the minimum requirements like a public registered and valid server name for the smtp server. I avoid any external SMTP service ... they can read all your emails ... There are many ready-to-use solutions, such as mailcow, which simplify the management of the mail server.