What MX record to register?

Question

Mail server

Hello!
Initial data: the server has an ISP manager. Domain in Reg.ru, there are DNS Cloudflare. Cloudflare has an A-record from the server IP.
In the ISP manager, I created a mail domain, a mailbox, set everything up, etc. All manuals go further to set up MX records in the "Domain names" section, and I do not have a domain there, since all records are stored in Cloudflare.
I do not understand what to do in the end?
If you register a domain in the "Domain names" section, then which DNS should be indicated first? And most importantly, how to properly configure the mail server? What MX to specify in Cloudflare?
Thanks for all the replies.

Answer 1

if I understand the problem correctly, then ...
MX is an additional record in DNS (the same domain names)
if all changes are made in Cloudflare, then you need to make a record there.
MX server - the name of the server that responds on port 25 to an incoming connection.
ISP manager - never used. if he requires these settings, then he probably thinks that HE controls the records in the DNS. If you don't, then you can probably ignore it.
before making records in DNS, it is better to check manually via telnet that the server accepts connections.