How to "not leak" the IP addresses of the server behind CloudFlare when sending mail from it via external SMTP?

Question

Mail server

There is a server behind CloudFlare, from which transactional emails go through SendPulse (or any other analogue) (about registration, password change, and so on). In the headers of the letters, the IP addresses of the server "shine", as a result of which it becomes pointless to hide it behind CloudFlare. What are the possible solutions?

Answer 1

It is obvious that not to send mail from it. Rent a VPS and drive mail from it, preferably through some kind of tunnel with gray addresses.
Or pull up a separate channel with other addresses for mail and drive through it

Answer 2

as a result, hiding it behind CloudFlare becomes pointless.

why? how to prove that the IP is the one for the CF?