By default, POP3 clients delete downloaded messages from the mail server. This makes it difficult to access e-mail on multiple computers, since downloaded messages are stored on the local computer. But usually a POP3 client can be configured to store copies of downloaded messages on the server.
POP3 client programs download messages to a single folder on the client computer (usually the Inbox folder). With the POP3 protocol, you cannot synchronize multiple folders on a mail server with multiple folders on a client computer. The POP3 protocol also does not support access to shared folders.
IMAP4 clients are much more flexible and usually offer more features than POP3 clients. By default, IMAP4 clients do not delete downloaded messages from the mail server. This behavior makes it easy to access e-mail messages from multiple computers.
IMAP4 clients support creating and accessing multiple e-mail folders on the e-mail server. For example, most IMAP4 clients can be configured to store a copy of sent items on the server so that these messages can be accessed from any computer.
IMAP4 supports additional features supported by most IMAP4 clients (for example, viewing message senders and subjects before downloading the entire message).
Sending and receiving options for POP3 and IMAP4 e-mail programs
POP3 and IMAP4 clients allow users to choose when they want to connect to a mail server to send and receive e-mail. This section discusses some of the more common connection options and provides some factors that users should consider when selecting the connection options available in their POP3 and IMAP4 e-mail clients.
Common configuration options
In most client programs that support the POP3 and IMAP4 protocols, you can set three such parameters:
Send and receive mail each time the e-mail program is started. If this setting is used, messages are sent and received only when the e-mail program is started.
Receive and send mail manually. If this option is used, mail is sent and received when you click the Send and Receive button in the client user interface.
Send and receive mail at a specified interval. If this option is used, the client program connects to the server at a specified interval to send messages and download new messages.
For more information about configuring these settings in the email program you are using, see the help documentation for that program.
Guidelines for selecting send and receive settings
By default, some e-mail programs do not save copies of messages on the server after delivery. If a user needs to view their messages using different programs or devices, it is recommended that a copy of the messages be saved on the server.
For clients with a persistent connection, the user can configure the email application to send and receive messages every specified minutes. Connecting to the email server at frequent intervals allows the user to keep the email application up to date with the most current information on the server.
However, if the client is not always connected to the Internet, the user can configure the e-mail application to send and receive messages manually.