Post Office Protocol Version 3 (POP3)

Post Office Protocol Version 3 (POP3) is an older protocol for retrieving emails from a mail server. You can imagine it like a mailbox: The emails are downloaded from the server and usually deleted there afterwards – similar to letters that you pick up from the mailbox and take home. POP3 was particularly useful in the early days of the internet, when emails were usually only retrieved on a single computer.

Nowadays, however, this behavior is rather detrimental: If an email is retrieved using POP3 on one device, it is no longer available on other devices. Synchronization—for example, of read or unread messages—also doesn't work. This is a major disadvantage, especially in the age of smartphones, tablets, and multiple workstations.

Although POP3 can still be useful in special situations – for example, when the internet connection is weak or when emails are intentionally only to be stored locally – in everyday life, the use of IMAP is recommended, as it enables central, synchronized management of messages.

Obsolete today: POP3 hardly makes sense in today's multi-device world. IMAP is more flexible, synchronizes between devices, and keeps messages on the server.

Classification in the OSI model:

• Application layer (Layer 7)
  POP3 operates at the application layer because it deals directly with retrieving and managing emails at the top level.