DigitalOcean has made a great guide to configure an email server that only sends email. If your email inbox are stored somewhere else, your server don’t need to receive and store any email. Configuring it to only send email is making it easier to maintain and less subject to hack/viruses.

Before reading the guide, I’ve created 2 subdomains that points to my server and I will use them in the tutorial.

Well in fact I created one twice, with an A type and AAA type to be sure both ipv4 and ipv6 are working. The A type must point to your server IPv4, the AAA type to your server IPv6. Let’s call it serv.site.com.

Once that’s done, I had to configure my reverse server IP. I found that in my server IP settings. For both IPv4 and IPv6, I’ve set the reverse to my previously created subdomain, serv.site.com. That will make Google and probably other email services happy. More on that on Google Documentation.

Next step, go and follow the tutorial. When entering the domain, I entered the subdomain I created, serv.site.com, not just site.com.

Go read the guide there