Hosting your own email system in its entirety out of your domain, i.e. becoming a mail host, does run into this, yes. Primarily around sending issues to other

Hosting your own email system in its entirety out of your domain, i.e. becoming a mail host, does run into this, yes. Primarily around sending issues to other major hosts - you can do it and email yourself / within your domain just fine, but Gmail will probably block your messages. Using your domain with an established provider has absolutely zero of those issues. That's super simple and works everywhere immediately.