IMAP OR POP3
When you set up your email client you are asked to select your email-server type. The common email clients support the following email servers.Post Office Protocol (POP3) server holds the emails until you download them from your server. When you download the emails it is permanently deleted from server. Use POP3 if you access emails form a particular system.
Internet Message Access Protocol (IMAP) server allows you to read, forward emails without downloading the email in your system. If you read or download any message then one copy of your email is always stored in email servers. It’s helpful for them who use multiple systems and want to access their messages.