How to set up a domain for mail?

Question

Email

1) The hoster has a DNS settings panel

At https://geektimes.ru/post/59417/ they suggest writing mail IN A 127.127.127.127 in the A-record, but for me it says "this is not a valid ip-address" and allows in A -records leave only IP
2) What to write in the name of the records. Write there it is necessary not a domain name and a server name. Let's say 56156.s.t4vps.eu and enter mail.56156.s.t4vps.eu in A and MX?
3) Question on MX

The MX record must point exactly to the A record of the mail server. Putting MX as a pointer to IP or CNAME is not correct.

So if in my A-record only IP allows me to enter then MX then it should refer to IP
4) On the server itself, in the Vesta panel, there is also a mail settings section. Then what to write there?

Answer 1

MX cannot contain an IP address, MX must contain A or CNAME, in your case
domain.ru. MX 0 mail.domain.ru.