What is a DNS ZONE file

DNS zone file of the website which plays important role for its functionality. For example,

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$ORIGIN domain.com. -------; authorize the start of this zone file in the name space
$TTL 1h-------------------------; the default expiration time of a resource record without its own TTL value
domain.com. IN SOA ns1.server.com. username.domain.com
(
2008090610-------------------- ; serial number of this zone file [Generally this number represents the day when its created]
86400--------------------------- ; slave refresh (1 day)
86400 ---------------------------; slave retry time in case of a problem (1 day)
172800 -------------------------- ; slave expiration time (4 weeks)
3600 -----------------------------; minimum caching time in case of failed look ups (1 hour)
)

domain.com. NS ns1.server.com. -----------------; nameserver for domain.com
domain.com. NS ns2.server.com. -----------------; backup nameserver for domain.com
domain.com. MX 10 mail.domain.com. ----------; mailserver for domain.com
domain.com. A 10.0.0.1 ---------------------------- ; IP address pointing to Server
www CNAME ----------------------------------------; "www.domain.com" is an alias for "domain.com"
------------------------------------------------------------------------------------------------

Along with above records we need PTR & SPF records as well which resolves IP addresses into host names.

One common misconception about PTR records is that they are for domain names. The domain has to have one IP to make sure your emails are not rejected by other mail servers. The fact is that PTR records are for IP addresses and not for domain names. This means that if you are using one server to send emails you don’t have to worry about your PTR record if the server is already set with IP addresses. If your mail server already has a PTR record created then your mail would rarely be blocked.

Due to the reason of a significant majority of Spam comes from forged addresses, a new Sender Policy Framework (SPF) standard is being implemented by a number of ISPs and mail hosts including Hotmail, Yahoo, AOL, etc. Those providers have begun to require SPF to allow mail through their networks. So Mail servers will require SPF records for their domains if they want their mail to be accepted by those providers.

No action is required on user part as long as the Server where site is hosted has DNS with PTR and SPF records created.