Density is defined as how thick or thin you want your hair to be. The standard and most popular choice is 130% which is Medium Density. You can see examples of the density - Click Here.
Google's Gmail Web-based email service runs on the Internet Message Access Protocol system, but it also offers Post Office Protocol mail server access.
The HTTP protocol is not a protocol dedicated for email communications, but it can be used for accessing your mailbox. Also called web based email, this protocol can be used to compose or retrieve emails from an your account. Hotmail is a good example of using HTTP as an email protocol.