IMAP, which stands for Internet Message Access Protocol, is a method for retrieving email messages from a mail server. With an IMAP email account, the email software does not download the messages to the local computer hard drive, but instead allows the user to read the messages directly from the server.
Because IMAP does not download or store the email messages on the local machine, users can access their email from multiple locations without fear of leaving read messages on someone else's computer. IMAP also benefits from being a protocol, not a proprietary software product, and can be customized to meet a company's unique needs.
An IMAP email client is necessary to retrieve mail from an IMAP mail server account. The user launches the client on his hard drive, which then connects to the remote mail server so the user can view his message inbox.
POP/POP3 is the Post Office Protocol method for retrieving email messages and is best suited for those who use the same computer to read their mail. Like IMAP, it uses a client to access the mail server, but the messages are copied to the local hard drive for offline reading and deleted from the mail server.
IMAP is ideal for shared mailboxes, such as those used for general inquiries from Contact Us web pages. Multiple people can log in to respond to the messages in the same box and immediately see in real time what messages their co-workers have already read and replied to without compromising the messages in the box.
Mail Box Quotas
Because IMAP does not automatically delete messages from the mail server when a user connects to read them, mailbox quotas are used to force users to delete their old messages and free up disk space for new messages. The mail server can be configured to notify users when they are close to exceeding their quota so actions can be taken to prevent mail delivery interruptions.