Chapter 2, Problem P17P

a)

Program Plan Intro

UIDL POP3 Command:

UIDL stands for Unique-Id Listing.

• The fact that optional UIDL command is supported is indicated by the UIDL capability.
• A unique number to each incoming mail message are assigned by POP3 servers.
• When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
• The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
• The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.

Given transaction:

Suppose one has configured their POP mail client to operate in the download-and-delete mode. The transaction is given as below:

C: list (client asks server to list the size of each of the stored messages)

S: 1 498 (Server lists the size of message 1)

S: 2 912 (Server lists the size of message 2)

S: .

C: retr 1 (Client requests to read message 1)

S: blah blah …  (Sends message 1)

S: ………blah

S: .

b)

Program Plan Intro

UIDL POP3 Command:

UIDL stands for Unique-Id Listing.

• The fact that optional UIDL command is supported is indicated by the UIDL capability.
• A unique number to each incoming mail message are assigned by POP3 servers.
• When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
• The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
• The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.

Given transaction:

Suppose one has configured their POP mail client to operate in the download-and-keep mode. The transaction is given as below:

C: list (client asks server to list the size of each of the stored messages)

S: 1 498 (Server lists the size of message 1)

S: 2 912 (Server lists the size of message 2)

S: .

C: retr 1 (Client requests to read message 1)

S: blah blah …  (Sends message 1)

S: ………blah

S: .

c)

Program Plan Intro

UIDL POP3 Command:

UIDL stands for Unique-Id Listing.

• The fact that optional UIDL command is supported is indicated by the UIDL capability.
• A unique number to each incoming mail message are assigned by POP3 servers.
• When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
• The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
• The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.

Given transaction:

Suppose one configured the POP mail client to operate in the download-and-keep mode. Then using the transcript in part b, suppose one retrieves messages 1 and 2, exit POP, and then five minutes later can again access POP to retrieve new e-mail. The given transaction is:

C: list (client asks server to list the size of each of the stored messages)

S: 1 498 (Server lists the size of message 1)

S: 2 912 (Server lists the size of message 2)

S: .

C: retr 1 (Client requests to read message 1)

S: blah blah …  (Sends message 1)

S: ………blah

S: .

C: retr 2

S: blah blah …

S: ………..blah

S: .

C: quit

S: +OK POP3 server signing off