IMAP Protocol for Email Retrieval
IMAP stands for Internet Message Access Protocol. It is an internet protocol at the application layer which uses port 143. The purpose of IMAP is to allow a local client computer to access email remotely from a server as though the emails were stored locally. IMAP version 4 is the current version (commonly called IMAP4). Along with POP3, IMAP4 are the two most widely used email protocols and all email clients support these two protocols.
All web hosts support the IMAP or IMAP4 protocol for email retrieval and most also support POP3. IMAP is very similar to POP3 but it has some extra features which is making it the more preferred choice in the modern day. Such distinguishing features include the ability to download emails on more than one computer whilst leaving a copy of the email on the server. POP3 does not allow this; once the emails have been downloaded to one computer, they can not download to another and will usually be deleted from the server (unless the server administrator specifies otherwise).
Advantates of IMAP email
Some of the advantages of IMAP over POP3 include longer connections to the server. POP3 usually only connects for the time required to download the email messages. IMAP stays connected if the user interface remains active. This can translate into faster download times for large messages.
Another advantage IMAP has over POP3 is that multiple clients can connect to the same mail box at the same time. POP3 only allows one client to connect to the server to get the email messages. IMAP is much more advanced in this department and this is a major reason for its increasing popularity amongst server administrators.
IMAP4 can ask the server to search for certain messages that meet particular criteria. These server side searches are not available with POP3. The benefit of this function is that the clients do not have to download every single message in an email box just to perform these searches (they can be searched through whilst still on the server).
IMAP4 clients are able to also create more than one mailbox on the one server. It has the ability to create, delete and rename mailboxes (folders) and email messages can be moved between these mailboxes. The benefit of this IMAP feature is the ability to provide access to public folders as well as shared folders. This makes for a much more complete and advanced email experience.