2.3

Question 1

What is a user agent?

Answer 1

allows people to compose, edit and read mail

i.e Outlook

outgoing, incoming messages stored on server

Question 2

What is a mail server?

Answer 2

mailbox contains incoming messages for user
message queue of outgoing mail messages
SMTP protocol between mail servers to send email messages
-client: sending mail server
-“server”:receiving mail server

uses TCP to reliably transfer email from client to server, port 25

Question 3

What are the 3 phases of SMTP transfer?

Answer 3

handshaking
transfer of messages
closure

Question 4

How does SMTP compare to HTTP?

Answer 4

HTTP: pull
SMTP:push

both have ASCII command/response interaction, status codes

HTTP: each object encapsulated in its own response message
SMTP: multiple objects sent in multipart message

Question 5

What are the 3 mail access protocols? (used to retrieve mail from server, SMTP deliver’s mail to receiver’s server)

Answer 5

POP: Post Office Protocol, authorization and download of mail
IMAP: Internet Mail Access protocol, more features than pop including manipulation of stored messages
HTTP: gmail, Hotmail, Yahoo etc

Question 6

What are the phases of the POP3 protocol?

Answer 6

authorization phase:
client commands user, pass
server either responds with okay or error depending

transaction phases:
client: list message numbers 
retrieve message by number 
delete 
quit

Question 7

Differences between POP3 and IMAP?

Answer 7

POP3 has download/delete mode that prevents user from re-reading messages
also has “downloads and keep” mode copies of messages on different clients
POP3 is stateless across sesions

IMAP keeps all messages in server
keeps user state across sessions(includes folders that it allows users to create)