Simple Mail Transfer Protocol
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This document provides an overview of the Simple Mail Transfer Protocol (SMTP). It discusses how SMTP clients and servers work, how messages are sent to SMTP servers using either relaying or DNS, the SMTP communication model involving connection establishment, message transfer, and connection termination. It also describes mail processing involving envelopes and headers, status codes, and special features like mail forwarding, gatewaying, and relaying. Limitations of SMTP are also noted.
Simple Mail Transfer Protocol
- 1. SUBMITTED BY: RAJAN PANDEY 0505CS081036 Simple Mail Transfer Protocol
- 2. INTRODUCTION SMTP clients and servers have two main components User Agents – Prepares the message, encloses it in an envelope. (ex. Thunderbird, Eudora) Mail Transfer Agent – Transfers the mail across the internet (ex. Sendmail, Exim) Analogous to the postal system in many ways
- 3. HOW MESSAGES ARE SENT TO SMTP SERVER? E-mail communication using Relaying Used during initial days of SMTP. SMTP routing information is included along with E-mail address. Problem with this method. Using DNS This method is used at present. The senders SMTP server makes the use of DNS to find MX record of the domain to which the E-mail is to be sent.
- 7. Mail is a text file Envelope – sender address receiver address other information Message – Mail Header – defines the sender, the receiver, the subject of the message, and other information Mail Body – Contains the actual information in the message
- 8. Status Codes The Server responds with a 3 digit code that may be followed by text info 2## - Success 3## - Command can be accepted with more information 4## - Command was rejected, but error condition is temporary 5## - Command rejected, Bad User!
- 10. MESSAGE PROGRESS
- 12. SPECIAL FEATURES Mail Forwarding: SMTP server may agree to accept e-mail for non-local mailbox and forward it to the appropriate destination. Mail Gatewaying: SMTP servers can be implemented as e- mail gateways which can translate TCP/IP email in a suitable form for some another e-mail system and vice-versa. Mail Relaying: SMTP includes the ability to relay mail from one server to another, as explained earlier, provided certain conditions are met. Address Debugging: VRFY command allows the client to ask the sender to verify address of recipient without sending mail to recipient. Mailing List Expansion: EXPN command allows to expand mailing list.
- 13. LIMITATIONS • Security matters for SMTP are worse. • Its usefulness is limited by its simplicity. • Transmission of executable files and binary files using SMTP is not possible without converting into text files. Use MIME to send mail in other format. • It cannot transmit text data that contains national language characters. These national language characters use 8-bit codes with values of 128 decimal or more. • It is limited to 7-bit ASCII characters only. • SMTP servers may reject mail messages beyond some specific length.
- 14. THANK YOU “Wish you have a Great Time Ahead” RAJAN PANDEY