How your email program gets the mail
If you use email, I'm sure you've heard someone talking about "POP access" or were told to configure the "POP server" in your email client. Simply put, POP (Post Office Protocol) is used to retrieve e-mail from a mail server.
Most e-mail applications use POP, of which there are two versions:
- POP2, a standard in the mid-1980s, requires SMTP to send messages.
- POP3, a newer version can be used with or without SMTP. POP3 allows e-mails to be downloaded from the server's inbox to your computer. In addition, your emails are available even when you're not connected to the server.
It's important to note that IMAP, (Internet Message Access Protocol) provides more complete remote access to traditional email.
In the past, less Internet Service Providers (ISPs) supported IMAP because of a large amount of the storage space needed on the ISP's hardware. Today, e-mail clients support POP, but also employ IMAP support.
The Purpose of Post Office Protocol
If somebody sends you an email it usually cannot be delivered directly to your computer. The message has to be stored somewhere, though. It has to be stored in a place where you can pick it up easily. Your ISP (Internet Service Provider) is online 24 hours per day seven days of the week. It receives the message from you and keeps it until you download it.
Let's suppose your email address is email@example.com. As your ISP's mail server receives an email from the internet it will look at each message, and if it finds one addressed to firstname.lastname@example.org that message will be filed to a folder reserved for your mail.
This folder is where the message is kept until you retrieve it.
What the Post Office Protocol Allows You to Do
Things that can be done via the POP include:
- Retrieve mail from an ISP and delete it on the server.
- Retrieve mail from an ISP and let it remain on the server.
- Ask whether new mail has arrived.
- Peek at a few lines of a message to see whether it is worth retrieving.
If you leave all your mail on the server, it will pile up there and eventually lead to a full mailbox. When your mailbox is full, nobody will be able to send you email.