When you send an e-mail, first your e-mail client software forwards the message to an e-mail server. When an e-mail message is sent through the Internet, the sending mail transfer agent (MTA) queries the DNS for MX records of recipient's domain name.
Reverse DNS (rDNS) is the opposite of the DNS. The DNS is queried for the IP address of a certain hostname. In reverse DNS, the hostname is returned for a certain IP address.
When an email is sent or received, there is no clear indication that the email is authentic or if it was sent from a validated sender address or domain. One way to improve email security is the DMARC standard.
DKIM validates a domain name identity that is associated with a message through cryptographic authentication. DKIM attaches a new domain name identifier to a message's header to validate authorization for its presence. The identifier is independent of any other identifier in the message.
The Sender Policy Framework (SPF) prevents sender address forgery. It protects the envelope sender address, which is used for the delivery of messages. SPF allows the owner of a domain to specify mail sending policy like which mail servers they use to send mail from their domain.
Suppose you have a website example.com, it can be accessed in two ways.
Before the domain name system was implemented, computers used to connect to each other via IP addresses. The domain name system attaches a unique name to this number so that site visitors can easily remember and return to web addresses.
DNS stands for Domain Name System. It is used to point memorable domain name towards the IP address of the server. This allows you to change web hosting without changing your domain name. Each website has a specific IP address, and the DNS records pair that IP address to the domain.