richnrockville is correct - IMAP and POP are exact opposites of each other. What POP does is physically download/move your email messages to the device you are using. Unless you specifically tell it to "Leave messages on the server" your email client will delete the emails you read from the server when it downloads them to your device. That means that once you read a message on one device it is no longer available on your email server to be read by any other device.
IMAP is just the opposite: by default it does not delete messages at all. What an IMAP server does is create a set of directories on the server to hold your incoming, saved, sent, junk, etc. emails. Your email client makes it look like those folders are on your local device, but they are actually on the email server.
The benefit of IMAP is that is you have several different devices for reading email you can switch among them and everything stays the same for all of them. For instance, if you get your email on one device and delete some messages, they get put into the Deleted folder on the server. You can then go back, from a different device, and still see this deleted email by looking in the server's Deleted folder. The messages you did not delete will still appear in your Inbox no matter what device you use to access your email; the reason is that the emails were not downloaded/moved to the device you first used to read email.
Which method to use depends on how you use email. If you only use one device for email then POP is likely better because it lets your single device have complete control over what email is where. However, these days many people use multiple devices for doing email and in that case it is usually better to do IMAP because it centralizes control and essentially keeps everything in one place, thus giving you a consistent view of your email from whatever device you are using.
I just recalled deleting messages from my hotmail account and outlook. and later when i went to check it directly in hotmail it was missing 
