Week 6 Flashcards
What is a user agent for mail?
allows users to send/read messages.
What are the 3 major components of the Internet Mail System?
- User Agent
- Mail Server
- Simple Mail Transfer Protocol (SMTP)
What is a mail server?
A server that stores a users “mailbox” .
there can be multiple mailboxes in a mail server
What is the SMTP?
Allows to transfer mail from one mail server to another. Has both a client and server side –> for receiving mail from users and other mail servers, and for sending them to other mail servers
What does SMTP use to transfer mail? And what port number?
TCP, Port 25. It uses persistent connections.
Does SMTP use intermediate mail servers for sending mail?
No. It uses Direct Transfer.
What are the 3 phases of a SMTP transfer?
- handshake
- send/receive message
- close
Some restrictions of SMTP format?
- rrequires header and body to be in 7-bit ASCII
- uses persistent connections
How is HTTP and SMTP different?
HTTP has client pull, SMTP has client push
HTTP has each object encapsulated, SMTP has multiple objects
What are some stuff a client sends into SMTP?
- HELO [client’s hostname]
- MAIL FROM:
- RCPT TO:
- DATA
- QUIT
How does the client SMTP indicate the end of the mail?
A single period. “.”
What are the 2 ways to retrieve mail from a mail server?
- HTTP for web-based
- IMAP for mail clients
What is the DNS?
The Domain Name System
- a directory tha translates hostnames –> IP address
What are 2 ways to identify internet hosts?
- Host name
- IP address
What layer is the DNS implemented in?
App-Layer protocol.
hosts and servers communicate to resolve names.