I got this error message in mx toolbox: “Reverse DNS Resolution - No PTR Record found”
After that, I just run a test on dnsinspect, and it gave me this: “Reverse Entries for MX records - WARNING: Found mail servers with inconsistent reverse DNS entries. You should fix them if you are using those servers to send email.”
The important part of the phrase you quoted from their site, is the part that I bolded here:
The reality is that the majority of the larger providers (e.g. Google / Gmail, Microsoft (365, Outlook, Hotmail, …), and yes, even Cloudflare’s Email Routing too), have their INBOUND mail servers and OUTBOUND mail servers separated.
Those DNS checkers only see your INBOUND mail servers, and these INBOUND mail servers do not send mail out, and therefore, the phrase you quoted is making the statement falling apart.
There is technically no problem here, so just ignore it.