You should also consult the [DKIM documentation](#/dkim). DKIM allows yours mails not to be considered by spam by other mail service. In fact DKIM ask you to add an entry in your zone.
DNS lines for subdomains, XMPP and email does not work without a redirection from the domain name to the IP address (one line is enough) because they depend on it.
<divclass="alert alert-info"><b>To begin:</b> lines with "(Minimal)" are the minimal required DNS entries to make redirection work from the domain name to the IP adress, XMPP and email.</div>
<divclass="alert alert-warning"><b>Warning:</b><b>@</b> is the default domain name currently defined, some registrar (like OVH) does not accept it, so replace @ by your domain name (domain.tld**.**) with a dot at the end.</div>
All DNS lines above have `1800` value (30 minutes). It corresponds to [Time to live (TTL)](https://en.wikipedia.org/wiki/Time_to_live#DNS_records) which represents and indicate time, in seconds, during which the DNS line can be kept in the cache. After this time, the information must me considered obsolete and must be updated.