How to transfer letters from yandex to iredMail and set up a mail server?

Question

Domain Name System

iRedmail 0.9.8(Latest version), centos 7
1. What is the best way to transfer emails?
On Yandex - imap, on my server it has not yet been determined, while pop3 is configured, but if possible in the free version of iredmail.
1.1 To transfer letters, I see only the creation of a subdomain mail.mydomain.ru. not to lose letters. And at home to make the mail was moydomen.ru - is it possible to make such a division at all? Or do I need to make archives for users with mail with pens?
2. What protocol to use imap or pop3 in the future?
2.1 Is there a free version of Imap, how to enable it.
3. What and where should be configured to receive emails on your server?
3.1 The site is located with us, for mail with the same domain to work, do I need to tell the provider to make some changes? I understand correctly since the mail on Yandex means that the provider has settings to send letters to Yandex?
3.2 Do I need to register any DNS with me? Here I will be grateful for the article, which can really help me.
3.3 Do I need to forward ports for pop3, imap and smpt to my server from outside? Are there any other protocols that I missed?
3.4 For point 3 - here are the settings for Yandex, what needs to be changed there?

NS record on yandex
Host Type Record value Priority
email A external ip address
@ A external ip address
nx A external ip address
www A external ip address
mail CNAME domain.mail.yandex.net.
_xmpp-client._tcp.conference SRV 0 5222 domain-xmpp.ya.ru. 20
_xmpp-client._tcp.conference SRV 0 5222 domain-xmpp.yandex.net. 20
_xmpp-client._tcp SRV 0 5222 domain-xmpp.ya.ru. 20
_xmpp-client._tcp SRV 0 5222 domain-xmpp.yandex.net. 20
_xmpp-server._tcp.conference SRV 0 5269 domain-xmpp.ya.ru. 20
_xmpp-server._tcp.conference SRV 0 5269 domain-xmpp.yandex.net. 20
_xmpp-server._tcp SRV 0 5269 domain-xmpp.ya.ru. 20
_xmpp-server._tcp SRV 0 5269 domain-xmpp.yandex.net. 20
mail._domainkey TXT v=DKIM1; k=rsa; t=s; p=*KEY*
@ TXT v=spf1 redirect=_spf.yandex.ru
@ SOA dns1.yandex.net.
@NS dns1.yandex.net.
@NS dns2.yandex.net.
email MX email.domain name. 10
@ MX mx.yandex.ru. 10
nx MX nx.domain name. 10
PS. I have never had experience with mail servers, please tell me what you know about these issues. Thanks in advance.

Answer 1

well, I would say so
1. if time is pressing, hire a specialist
2. if not, create a test domain and try to set up a link postfix/postfixadmin/dovecot. It would be good if the server was dedicated and had a white address. Along the way, you will have to be imbued with DNS and the database. When the server is up and running, you can attach spf/dkim/rspamd/encryption/smtp-auth. As a result of these actions, you have an understanding of how everything works. Then you can also use imapsync and transfer mail.