What means pop3, smtp, imap?

All3 are internet protocols dedicated for emails.

-pop3(Post Office Protocol): used to download the email from the email server to the client and delete it from the server.

-smtp(Simple Mail Transfer Protocol): used to send the emails through your mailing server.

-imap(Internet Message Access Protocol): used to communicate with the email server to access the emails without deleting the emails from the server so different users can simultaneously access the mailbox as the emails are kept into the server.