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.
SMTP is the protocol used to <send> new mail regardless of what protocol is used to <retrieve> new email which is why POP3 and Imap accounts are shown as POP3/SMTP and Imap/SMTP account types in the Outlook account settings. All external internet email is sent using the SMTP protocol from an SMTP server.