POP3, IMAP and SMTP

POP3 & IMAP

POP3 and IMAP are two different email protocols, these protocols used to retrieve emails from a email server.

lets say we have email client like outlook installed and it uses either of these two protocols to retrieve email from the mail server. the client can be installed on a computer, tablet or a mobile phone to access the emails from mail server by configuring either POP3 or IMAP.

there are few key differences between the two protocol

POP3 stands of Post Office Protocol 3

• This is simplest among the two, it only download the inbox mails from the server to clients inbox. it does not download any of the content from other folders on the server.
• By default it deletes the copy of the email from the server after successfully downloading it to the clients inbox.
• assume that we have two email clients accessing the same email account they can have different folders at client besides inbox.
• since the copy of the email gets deleted from the server, only one of the clients accessing the server will get the email other will miss it. however most of the email clients will have a setting to “leave the copy at the server” This helps other clients of the same account to access the same email from the server.

Pros

• we can access emails offline even if we dont have internet connection since the emails gets downlaoded and stored at the client side.
• saves storage space on the server, since the emails gets deleted on the server after it is download at the client by default.

Cons

• we need to have backup plan of storing the email and access the emails from different clients.
• client device has more vulnerable of viruses and hacks than the server.

IMAP stands for Internet Message Access Protocol

• unlike POP3, IMAP syncup all the folders on the mail server at the clients. so every client will have same folders and custom folders besides inbox.
• it does not delete the copy of the email at the server so all the clients will be in sync at any given instance of time and gets caches at the client side.
• when we delete the mails from one client same emails gets deleted on the server and other client as well. because the all client cache gets refreshed all the time and in sync with the server.

Pros

• we can access the emails from multiple devices whether it is web email client or client software installed on the device
• all the folders are synchronized between the devices

Cons

• emails can not be viewed with out an internet
• however some of the client software “allows to down load the email” along with caching to access them offline.

SMTP (SMTP/TCP)

SMTP stands for Simple Mail Transfer Protocol, used to “send” mails to people. on the other hand pop3 and IMAP are used to receive email from the server.

simple way to remember is SMTP “ Send Mail To People “

SMTP uses TCP as transport protocol, since the TCP is connection oriented protocol to make sure that the connection is established to the destination before sending the data packets and guaranteed mail delivery.

This is the reason when we send an email to the email which does not exist, we will get an “Mail Delivery Failed” error mail in the client mail box.

in conclusion we use both SMTP and POP3/IMAP to send and receive emails in client to client communication.