What is IMAP4
Internet Message Access Protocol version 4 (IMAP4) is an Internet messaging protocol that enables a client to access e-mail on a server instead of downloading it to the user's computer. IMAP4 is designed for an environment in which a user logs on to the server from several different workstations. In such an environment, downloading a user's mail to a specific computer is usually impractical because the user does not always use the same computer. For example, IMAP4 is widely used in universities where students connect to the mail server from different labs throughout the campus. Once connected, users can access their mailboxes as though their mail is stored locally. IMAP4 does not provide mail transport. Simple Mail Transfer Protocol (SMTP) provides this feature.
IMAP4 allows a client to access private messages and public folders on a server. Users with an IMAP4 client can access mail in their Exchange mailboxes without downloading the entire mailbox to a specific computer.
A single client can access multiple mailboxes to retrieve specific messages or portions of a message, such as an attachment. IMAP4 clients can also search a mailbox and store flags to identify messages that have been read.
You can configure your IMAP4 server to grant or deny access to specific computers, groups of computers, or domains. You can grant or deny access to a single computer based on an IP address, or override IMAP4 access on a per-user basis. A group of computers can either receive or be denied access based on their subnet address and subnet mask. You can also control access to an entire domain by specifying the domain name.