POP

POP can be thought of as a "store-and-forward" service.

Post Office Protocol is the primary protocol behind email communication.

POP works through a supporting email software client that integrates POP for connecting to the

remote email server and downloading email messages to the recipient’s computer machine.

POP uses the TCP/IP protocol stack for network connection and works with Simple Mail Transfer

Protocol (SMTP) for end-to-end email communication,

where POP pulls messages and SMTP pushes them to the server. As of 2012, Post Office

Protocol is in its third version known as POP 3 and is commonly used in most email client/server

communication architecture.

POP3 (Post Office Protocol 3)

POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-

mail.

POP3 is a client/server protocol in which e-mail is received and held for you by your Internet

server.

Periodically, you (or your client e-mail receiver) check your mail-box on the server and download

any mail, probably using POP3.

This standard protocol is built into most popular e-mail products, such as Eudora and Outlook

Express.

It's also built into the Netscape and Microsoft Internet Explorer browsers.

POP3 is designed to delete mail on the server as soon as the user has downloaded it.

However, some implementations allow users or an administrator to specify that mail be saved

for some period of time.

POP3 is an Internet protocol for retrieving e-mail.

When using POP3 to check e-mail, an e-mail client connects to the POP3 server and downloads

e-mail messages to your local machine.

In most cases, the client then deletes the messages from the server.

Compared to IMAP

IMAP is a newer, more capable protocol than POP3. POP3's simplicity makes developing e-mail clients

for it easier, however this also means that several features found in IMAP are unavailable in POP3.

Because POP3 downloads and then deletes message from the server, it should only be used in situations

where the user only wants his or her e-mail to be on a single computer (and one on which the user will

do regular data backups).

IMAP, on the other hand, leaves e-mail messages securely on the server,

so it is useful in situations where the user might want to check his or her e-mail from more than

one location.

IMAP:

An alternative protocol is Internet Message Access Protocol (IMAP).

IMAP provides the user more capabilities for retaining e-mail on the server and for organizing it

in folders on the server.

IMAP can be thought of as a remote file server.

POP and IMAP deal with the receiving of e-mail and are not to be confused with the Simple Mail

Transfer Protocol (SMTP), a protocol for transferring e-mail across the Internet.

You send e-mail with SMTP and a mail handler receives it on your recipient's behalf. Then the

mail is read using POP or IMAP.

The conventional port number for POP3 is 110.

What are POP3 and IMAP4 protocols?

Keio Mail is designed to be used as a Web mail system. However, some users might want to

send and receive email using a different email client. To meet this demand, Keio Mail can be

also used with the POP3 and IMAP4 protocols. A brief explanation of the POP3 and IMAP4

protocols is provided here. Please use these protocols as desired.

Protocol Advantages Drawbacks

POP3

Email is retrieved from the server and

stored on the PC. Therefore, once email has

been received, it can be read offline (i.e.

without connecting to the internet). This is

most effective when the internet connection

is not reliable.

The user must receive email on each PC

and the reception conditions might differ

between PCs. If the user forgets to keep

messages on the server, he/she might not

be able to receive the messages on a

different PC.

IMAP4

Email on the server can be directly accessed

and the same email environment is

available on each PC. It can coordinate with

the status of Web mail. It is most effective

when the internet connection is relatively

reliable.

Email cannot be read without an internet

connection (some email clients store the

messages in a cache and they can be read

offline). One must ensure that there is

enough free disk space on the server.