The following sections provide more detailed explanation of how POP3 and IMAP4 behave and what their strengths and weaknesses are.
The POP3 protocol is simply a standard way of accessing a mail server and downloading your mail from this server. POP3 provides support for getting mail from one folder: the Mailbox. It does not support multiple folders or keep mail organized between multiple folders on the server side. By default, when you set up a POP3 account and download your mail, it is removed from the server. Hence, your mail now exists exclusively on the machine where you are running the POP3 client. Also, by default, the POP3 protocol downloads the entire message regardless of size when you connect. The POP3 protocol does the following:
Changes made to mail items on the local client (deleting mail) are not replicated back up to the server-side mailbox.
You can configure the client to leave messages on the server. This capability may be useful if you will be accessing your mailbox from other clients such as a web browser that communicates directly with the Internet server. Figure D.1 displays the Advanced tab where you can configure GroupWise to leave mail on the server.
Figure D.1. When configuring a POP account, you can leave the mail on the server
POP3 does not support server-side folders. This means that the only folder you can download via a POP connection is the Mailbox folder. If you have created additional folders in your Internet account, you will not be able to synchronize them with a POP connection.
The IMAP4 protocol is also a standard way of accessing a mail server and downloading your mail from this server. IMAP is a newer, more robust, and feature-rich protocol. It has support for multiple folders on the server side and, by default, does not remove the mail from the server when a connection is made and mail downloaded. IMAP downloads only the header of the mail message by default. This way, you can see the Subject, From, and Size fields of the message. If the message is large, you will know how large it is before reading it and the rest of the mail message is downloaded. An IMAP4 account does the following:
Messages stay on the server and are not removed from the server when you synchronize your client.
When you synchronize, only the headers of the mail messages are downloaded. The header contains the From, To, and Subject fields and the size of the entire message. When you open a message, it is then downloaded to your local computer in its entirety, meaning the message body and any attachments. This allows you to potentially delete mail without having to download the entire message. This capability can be useful if you receive a great deal of junk mail.
IMAP is designed to keep the local message store in sync with the server side. Hence, if you drag an email item to a different folder from the client, it will be synchronized up to the server and reflect the change there.
Performance over a dial-up connection is somewhat faster on IMAP compared to a POP connection.
All folders are synchronized, not just the Mailbox folder. This allows you to organize mail in folders on the server and see the same folder structure from your GroupWise client through the IMAP account.
Losing your server connection can cause problems. Because the initial sync downloads just the message headers, if you lose the connection when you are browsing through your mail, you will not be able to read new mail. Any old mail that has already been downloaded is accessible, of course.