POP3 (or) Post Office Protocol

1) What is known as POP3 or Post Office Protocol?  

Post Office Protocol version 3 (POP3) is an Internet protocol that allows a POP3 client to download e-mail from a server. This protocol works well for computers that cannot maintain a continuous connection to a server.

2) What are the similarities between IMAP4 and POP3?

Both IMAP4 and POP3 are Internet messaging protocols that allow clients to access their mail.

3) What are the differences between IMAP4 and POP3?

The difference between these protocols is the location where the client manipulates the messages. IMAP4 allows a client to access and manage mail on a server. POP3 allows a client to download e-mail from an Inbox on a server to the client computer, where messages are managed.

Unlike IMAP4, POP3 does not allow users to manipulate messages on the server. Mail simply downloads messages to the client where they are managed. POP3 provides access to a user's Inbox only; it does not support access to public folders.

4) Where POP3 manages the work?  

All management of POP3 user mailboxes is performed in the Microsoft Active Directory directory service. In previous versions of Exchange, Exchange used its own database to hold directory information, and managed recipients through the Exchange administrator. In Exchange 2000, Active Directory can hold all messaging directory data. Because a separate directory for Exchange is not necessary, all mailbox administration is coordinated in Directory Service Manager. After installing System Manager on a computer running Windows 2000, a set of extensions is added to the standard Active Directory console. This allows an Exchange mailbox to be created when a new user account is defined in Active Directory Users and Computers.

Only users with Windows 2000 accounts can have a mailbox, and send and receive mail. If an account is mail-enabled but not mailbox-enabled, users can only send mail. Mailbox-enabled users can also receive mail and configure additional settings.

5) How to manage Multiple POP3 servers?

A unified namespace provides easier administration of multiple POP3 servers. For example, if you have three separate computers running a POP3 virtual server, you normally divide the user load by configuring certain users to connect to POP3Server1, other users to connect to POP3Server2, and still other users to connect to POP3Server3. If all POP3 servers are part of a front-end/back-end configuration, there is one name that provides user access to all POP3 servers in your configuration. You can configure clients to connect using the same POP3Server. You can use software load balancing or hardware load balancing to randomly distribute the load to any of the three POP3 servers. When you want to move a user's mailbox from one server to another, the client does not need to reconfigure the name of the server it logs on to. As your user population grows, you can add more computers to the front-end bank of servers without reconfiguring the clients.

6) Working POP3 with SSL (Secure Sockets Layer)? How do you reduce the load on back-end server?

When connections are made using Secure Sockets Layer (SSL), information is encrypted and decrypted. The encryption and decryption process is processor intensive and can affect performance. If your POP3 virtual servers are deployed in a front-end/back-end configuration, the front-end servers can process encryption with the client. When the front-end server and back-end server communicate, they do so without the network bandwidth load of SSL encryption. This reduces the load on the back-end server.