[Mashiro]

There's a record that wasn't in the DNS Records for my domain in VestaCP - CName - I've added that too with Yandex CName - was that OK to do?

Not entirely necessary. When you open mail.yourdomain.ext it will redirect to domain.mail.yandex.net where you can login with your e-mail addresses. That's all. Just a redirection from your domain to the Yandex.Connect webmail client.


DMARC - I have no idea about this. Yandex.Connect doesn't seem to support it as it has no DMARC record in the list. The one configured by VestaCP by default has no real meaning because it is configured as "none". So the record itself is useless without a proper value and a mail provider that doesn't support DMARC.


Given that you host mail off site you can delete the POP3, IMAP and SMTP records actually as they're not necessary and won't work anyway with Yandex.Connect.