There are 3 specific protocols involved to facilitate the outgoing and incoming email messages, and they are briefly listed below.

• SMTP (Simple Mail Transfer Protocol) - It is utilized to handle the sending of emails. 
  • Port 25
• POP3 (Post Office Protocol) - Is responsible transferring email between a client and a mail server. 
  • Port 995
• IMAP (Internet Message Access Protocol) - Is responsible transferring email between a client and a mail server.
  • Port 993