1) SMTP Protocol: 

  • The SMTP (Simple Mail Transfer Protocol) defines rules to send message over internet. 
  • SMTP specifies the standard that helps the email client to send message to the mail server . 
  • SMTP sends message in ASCII character set to the mail server. 
  • The SMTP protocol can only be used to send emails, not to receive them. 
  • In case, message cannot be delivered, an error report is sent to the sender which makes SMTP a reliable protocol. 
  • When you send e-mail, your e-mail client sends it to your e-mail server which further contacts the recipient mail server using SMTP client.
  • The exchange of commands between servers is carried out without intervention of any user.

2) POP Protocol: 

  • The POP (Post Office Protocol 3) protocol provides a simple way for users to access mailboxes and download messages to their computers. 
  • When using the POP protocol all your eMail messages will be downloaded from the mail server to your local computer. 
  • POP has various versions like POP , POP2 , POP3 . Among them POP3 is latest one. 
  • POP3 allows you to download email messages on your local computer and read them even when you are offline. 
  • Note, that when you use POP3 to connect to your email account, messages are downloaded locally and removed from the email server. 
  • This means that if you access your account from multiple locations, that may not be the best option for you. 
  • On the other hand, if you use POP3, your messages are stored on your local computer, which reduces the space your email account uses on your web server. 
  • POP does not allow search facility.
  • It is not suitable for accessing non mail data.
  • POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.


3) IMAP Protocol: 

  • IMAP (Internet Message/mail Access Protocol) –Like POP , IMAP is also a standard protocol for accessing e-mail from your local server. 
  • Using IMAP , you can view your email message located on your email server. 
  • It enables us to take any action such as downloading, delete the mail without reading the mail.It enables us to create, manipulate and delete remote message folders called mail boxes. 
  • Only if you request to read a specific email message will it be downloaded from the server. 
  • You can also create and manipulate folders or mailboxes on the server, delete messages etc. 
  • Its latest version is IMAP4 . 
  • IMAP4 has similar feature like POP3 but it also has some additional features like search for keywords in the email message.