This is a question often asked. I need to start using Outlook Express to check my GMail, but what should I use - Pop3 or Imap?
Before we get into the comparison of both, lets look at them individually.
IMAP - IMAP stands for Internet Message Access Protocol. It is a protocol for accessing email from your local computer. It is a client/server protocol in which e-mail is received and held for you on the servers. You can view just the header information, which includes the sender and subject of the letter, allowing you to decide whether to download the message or not.
POP3 - POP3 stands for Post Office Protocol 3. It can act as a standard protocol to receive email on your client, or as a client/server protocol. The mail is stored on the server, until you download it on your client. Once downloaded the mail gets deleted from the server.