POP3 is an older protocol that was originally designed to be used on only one computer. Unlike modern protocols that use two-way synchronization, POP3 only supports one-way email synchronization, only allowing users to download emails from a server to a client. Because of this, POP3 accounts lack most of the basic functionality that can be found in more modern services, such as:

• The ability to mark a message as read on multiple devices, meaning that every time a user downloads an email onto a different device using POP, it will appear as a new message instead of indicating it was read on another device.

• The ability to send items from multiple devices. Sent items cannot be synchronized using POP and can only be saved on the device from which they originated.

• Having the ability for emails to be pushed to your device as they arrive. Instead, your device must be set up to automatically check your email server periodically to see if new messages have been received.

• Having special folders created or settings set on one device available on all devices using that email account. Using POP, users must manually create or set these individually on all their devices. This means, if users organize their emails on one device, they’ll need to do it again for every other device that uses that POP email account.