Tutorial-21. Study of below given protocol:

(i)SMTP:-

Simple Mail Transfer Protocol (SMTP) is an internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks.

SMTP uses TCP Port 25. It uses Layer no. 3 (Network Layer). SMTP connections secured by SSL are known by the

shorthand SMTPS. SMTP defined by RFC 821 and updated by standard RFC

5321. While electronic mail servers and other mail transfer agents

use SMTP to send and receive mail messages, user-level client mail applications typically use SMTP only for sending messages to a mail server for relaying.

(ii) IMAP:-

Internet Message Access Protocol (IMAP) is a protocol for e-mail retrieval.

IMAP is an Application Layer Internet protocol that allows an e-mail client to access e-mail on a remote mail server.

An IMAP server typically listens on well-known Port 143. IMAP over SSL (IMAPS) is assigned well-known port

number 993. IMAP supports both on-line and off-line modes of

operation.

(iii) POP3:-

Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection.

POP and IMAP are the two most prevalent Internet standard protocols for e-mail retrieval, Virtually all modern e-mail clients and servers support both.

Most webmail service providers such as Gmail and Yahoo! Mail provide both an IMAP and POP3 service.

POP supports simple download-and-delete requirements for access to remote mailboxes.

A POP3 server listens on well-known port110.

(iv) DNS:-

The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.

It associates various information with domain names assigned to each of the participating entities.

Most prominently, it translates easily memorized domain names to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide.

Domain Name System is an essential component of the functionality of the Internet.

For example, the domain name www.example.com translates to the addresses 192.0.43.10 (IPv4) and 2001:500:88:200::10 (IPv6).