Help with changing DNS server configuration file on Linux?

Question

Domain Name System

Hello dear experts!
I honestly admit that I do not understand this issue, but as I understand it, the question is very simple.
We want to migrate our mail server to Mail.ru business mail and we need to make changes to our own DNS server on lincus.
Here is the record we need to add (naturally changed the token to a fictitious one)
Domain/subdomain name: @
Record type: TXT
Value (all in bold):
mailru-domain: V324SFiovw123e
Our DNS server configuration file (I don’t understand the issue as much as that, just in case, for privacy purposes, he changed the IP addresses to arbitrary ones, and replaced the companies in the domains with companyname1, companyname2, and so on.

$TTL 3D
@       IN      SOA     ns.companyname1.spb.ru. root.companyname1.spb.ru. (
                          2015071901      ; serial, todays date + todays serial
                          600              ; refresh, seconds
                          200              ; retry, seconds
                          4W              ; expire, seconds
                          1D )            ; minimum, seconds
;
                  NS      ns              ; Inet Address of name server
                  NS      ns.companyname2.net.
                  NS      ns2.companyname3.net.
                  NS      ns3.companyname3.net.
                  MX      10 mail.companyname1.spb.ru.     ; Primary Mail Exchanger
                  MX      20 mail2.companyname1.spb.ru.   ; Secondary Mail Exchanger
                  MX      30 mail3.companyname1.spb.ru.   ; Secondary Mail Exchanger
;
localhost       A       127.0.0.1
ns              A       190.3.176.84
mail            A       190.3.176.84
mail2           A       190.3.176.84
mail3           A       190.3.176.84
web             A       190.3.176.84
www             A       240.26.34.156
companyname1.spb.ru.     A       190.3.176.84

As far as I understand, when making changes to this file, you need to change the date and serial to the current day on which the changes are made, but how to correctly add a TXT record with a token from the Mail.ru Group and in what place, I don’t understand, google didn’t help
Help, please. Thanks in advance.

Answer 1

first you need to add what you are asked to
add to the @ IN TXT file
"mailru-domain: V324SFiovw123e"
then increase the serial in the soa record
@ IN SOA ns.companyname1.spb.ru. root.companyname1.spb.ru. (
2018110201 ; serial, todays date + todays serial
600 ; refresh, seconds
200 ; retry, seconds
4W ; expire, seconds
1D ) ; minimum, seconds restart
bind
You will be authorized on mail.ru, then you will need to change the MX records of the domain according to the instructions mail.ru
PS. Standard advice: Hire an admin.

Answer 2

It is necessary to correct the lines, indicate the IP addresses that you received from mail.ru. And of course Serial)
mail A 190.3.176.84
mail2 A 190.3.176.84
mail3 A 190.3.176.84