Have you got an iPhone and a Gmail account? If so, you're probably using IMAP, and you may not even realize it. What's IMAP? It's an email protocol that has been around for many years, but is not nearly as well known as its counterpart, POP. First, the definitions:
POP, or POP3: Post Office Protocol 3, the most commonly used email protocol for retrieving remote email to a local client over a TCP/IP connection.
IMAP, or IMAP4: Internet Message Access Protocol, an email protocol for accessing email on a remote server using a local client over a TCP/IP connection.
While the two definitions seem very similar, take note of the difference. POP is used for retrieving email to the local client, whereas IMAP is used to access email located on a remote server.
When you use POP, your email comes in to you local client, and typically the remote version is purged. There is no concept of multiple clients having identical synchronized versions of your inbox and email folders.
When you use IMAP, your email actually lives on a remote server, and is not purged. You can access it with a local client, which downloads a copy of your messages, and synchronizes the contents of your local mail store to that of the server's. Changes that you make locally are reflected on the server, and if you wanted to you could connect with another device or email client that is capable of IMAP, and you will see exactly the same thing - all of your messages in your inbox and other folders will reflect exactly what is on the server.
Sounds pretty great, right? Well, yes. Most of us probably have some hardcore geek friend that has been extolling the virtues of IMAP for years, only to have it fall on deaf ears. Most of us have either never had the need for such synchronization, or have not had an IMAP capable mail provider.
This post's subtitle could be "Why 
