Have I configured the zone correctly?

Question

Domain Name System

I have a server with an IP, say 1.2.3.4 . There is a site named, for example, mydomain.ru .
The PTR for 1.2.3.4 points to mail.mydomain.ru . And mydomain.ru refers to 1.2.3.4 .
Have I configured the zone correctly?
Am I setting the MX record correctly?
I use, as you can see, Yandex DNS.
mail ______ A __________ 1.2.3.4
@ ________ A __________ 1.2.3.4
www ______ A __________ 1.2.3.4
@ ________ TXT _______ v=spf1 a mx ip4:1.2.3.4 ~all
@ ________ NS _________ dns1.yandex.net.
@ ________ NS ________ dns2.yandex.net.
@ ________ MX _______ mail.mydomain.ru. ten

Answer 1

Is the second MX with parameter 20 optional?

Answer 2

1.MX record is in the wrong format. It is necessary like this:
@ MX 10 mail
2.spf record I would have written differently:
@ ________ TXT _______ "v=spf1 ip4:1.2.3.4 -all"
This is more strict.
3. You can specify names in your domain without a domain part and without a trailing dot (see item 1), because The DNS server itself substitutes the domain name at the end if the name does not end with a dot.