MX records for subdomains with G Suite email

My main domain is all set with CloudFlare. Email goes through G Suite Google Workspace and I added DKIM and DMARC records for it. I have a subdomain and since it is a second level subdomain it is not set up with CloudFlare. Email for the subdomain, which is considered a “domain alias” by G Suite, is also handled by G Suite. It all works, but the G Suite domain administration is giving me an error message for the subdomain: “MX record validation failed.” Talked to G Suite support and they are telling me I need to set up MX records for the subdomain. Since the subdomain is not set up with CloudFlare I don’t know how to set up these MX records. Where would they go? Any ideas? Thank you!

That MX record needs to be on the name servers that respond for that subdomain. These are shown by looking for a NS record for sub.example.com, like at dnschecker.org

Thank you for replying. When I check for the subdomain, nothing comes up (the domain is at dara.ns.cloudflare.com and duke.ns.cloudflare.com). There are no MX records for the subdomain. From what I understood when we first set up with CloudFlare, the subdomain did not need MX records since it was a second level subdomain. That’s my puzzlement. G Suite wants me to add MX records for a subdomain, and according to CloudFlare, as long as the domain has MX records the subdomain doesn’t get its own MX records.

Where did it say this? Cloudflare DNS may give a warning if there are no MX records, but you need an MX record for whatever comes after the @ in your email address.

Maybe I misunderstood. Is the subdomain not set up somewhere else?

By default, all DNS requests for something.somethingelse.subdomain.example.com will use the same nameservers as configured for example.com unless you have delegated them to another name server. You would need to have NS records for subdomain.example.com configured in Cloudflare do do this.

I suspect that is not the case here, so you need to create the MX records on your Cloudflare account for the subdomain:

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OK. It’s becoming somewhat clearer (only somewhat though!). Thank you for responding.

The DNS subdomain’s records are on our server, accessible through cPanel, just like the domain’s records. The domain is also on CloudFlare and the DNS records are basically duplicated, as far as I can tell. The domain MX records point to aspmx.l.google.com, etc. The subdomain is not on CloudFlare, and although it still uses G Suite for email, the DNS records on the server do not include MX records for aspmx.l.google.com. Perhaps this is my error?

Thank you. Just to make sure I get it…

If I understand correctly, I will be adding the MX record for the subdomain under the DNS management of the domain on CloudFlare?

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