Differences between SMTP and POP

(a) The protocols themselves are different (SMTP and POP).

(b) SMTP accepts a message from an arbitrary sender; whereas POP server allows only a user to access his mailbox after the user authenticates himself (using a user id and password).

(c) SMTP server can transfer only email messages; whereas a POP server can also provide information about the mailbox contents (e.g. the number of unread mails, a list of sent mails, etc.).

Let us understand the whole process step by step.

I Suppose I have an email account named ASG on the domain ABC.com. Therefore, my email account is ASG@ABC.com. I want to send an email message to Atul, whose email id is Atul@mindspring.com. I compose the email message using an email client program on my computer and press the send button provided by the email program.

The SMTP client at ABC.corn takes the recipient's email address and makes two parts of it: (a) The recipient's name (Atul) and (b) The domain name (mindspring.com). If the recipient were in the same domain as the sender, the recipient's domain name would also have been ABC.com. In that case, the SMTP server's job would have been quite easy. But in this case, since the recipient's domain is not ABC.com, SMTP has to communicate with a different domain (that is, mindspring.com).

3. Using the DNS mechanism, SMTP at ABC.com requests for the IP address corresponding to the domain name mindspring.com. Either the DNS server knows it and therefore, does not need to make any further requests, or it requests for it with other DNS servers, and finally obtains the IP address.

4. Having obtained that IP address, SMTP at ABC.com now connects with the SMTP server at mindspring.corn using TCP/IP protocols. The port number for SMTP is pre determined. Therefore, now a TCP connection can be established.

5. Once the connection is established, SMTP at ABC.com sends the email message to the SMTP server at mindspring.com using TCP/IP (i.e. breaking the message into smaller packets, routing them, etc.). After the message is transferred, the SMTP client and the SMTP server break the connection. As we know, this is a virtual TCP connection. The message is sent as IP datagrams.

6. The SMTP sever at mindspring.corn now stores the email message in the mailbox designated for Atul. This mailbox can be accessed by both SMTP as well as POP servers, as we have seen earlier.

7. When Atul connects to the POP server at his domain the next time, using the POP client inside its email software, it asks the POP server if there are any new email messages for him. In response, the POP server sends a copy of this email message to his computer. Thus, the email reaches the ultimate destination.

This scheme offers the following main benefit:

The sender as well as the recipient need not be connected to the Internet all the time. The sender can compose the email message without needing to connect to the Internet. Only when the sender actually wants to send the message does he need to connect to the Internet. The same thing happens with the recipient. The recipient connects to the Internet only for receiving email messages using POP. Once the emails are downloaded onto his computer from the POP server, he can disconnect. Since the emails are already on his computer, he need not contact the POP server for reading them.

Domain Name Search