What is SMTP and POP3?

SMTP and POP3 are protocols used to facilitate email traffic between computers. Every time an email is sent it goes through a set of protocols that ensure security and allow conversation between the client and the host. SMTP is used along side of POP3 in a workplace environment. SMTP is short for Simple Mail Transfer Protocol and allows the email client to send emails to the server. Using port 25, SMTP connects to the email server and sends information to the server. The server receives the emails and processes where to send them.

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Another client attempting to access email will send a request to the mail server using POP3. POP3 is short for Post Office Protocol version 3. The server receives the request and sends the requested emails to the client using POP3. The emails are then stored on the client system’s hard drive.
An email provider such as hotmail.com would work like this.
To send email:

  1. The user goes to hotmail.com and enters personal login information.
  2. User composes email.
  3. User hits send.
  4. The email client sends the email to the mail server on port 25 using SMTP.
  5. The server receives the email and stores it on a hard drive.

To retrieve email:

  1. User goes to hotmail.com and enters personal login information.
  2. User requests email inbox.
  3. The email client sends a request to the SMTP server and uses POP3 to download the email from the server.
  4. The email information is stored on the local client’s hard drive.

SMTP is also used to send emails from one server to another. SMTP servers can understand simple text prompts, which allows users to type in commands directly to the server.
Commands:
HELO – introduce yourself to the server

EHLO – introduce yourself to the server and request extended mode

MAIL FROM: specify the sender

RCPT TO: specify the recipient

DATA – specify the body of the message

RSET – reset

QUIT – quit the session

HELP – help list

VRFY – verify an address

EXPN – expand an address

VERB – verbose
Other Windows E-mail clients use POP3 and SMTP configurations for single users and home situations. IMAP is another protocol that can be used in place of POP3. IMAP is useful when an email is shared among many users. An example of this might be a technical support team for a computer manufacturer.
SMTP and POP3 work together to provide convenient email services to clients.

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