POP3 and IMAP are two popular protocols used to configure mailboxes in mail client applications on desktop computers, mobile phones and tablets. What distinguishes these protocols from one another is the way each one handles messages on the server.

POP3 – The Downloader

When a mail client uses POP3 to connect to the server, messages are downloaded from the server to the client mail application. Users may configure their client to download and permanently delete messages from server or to download and to leave a copy of the messages on the server for a period of time.

IMAP – The Synchronizer

Unlike POP3, IMAP does not download messages from the server. Each time a user connects via IMAP, the mail client synchronizes with the server and displays message header information for messages that actually reside on the server. When you’re connected using IMAP, you’re essentially “working off” the server. All of your mail data and folders are synchronized between the client and the server.

This concept of working off the server and synchronization gives IMAP a huge advantage over POP3 when working on multiple devices.  Messages that have been “read” appear as read on all devices. Deleted messages only need to be deleted one time and not multiple times on each device. Additionally, a group of users that needs to access a single mailbox may work collectively, each accessing the mailbox from their own device and all viewing the same messages and folder structure.

When would it make sense to use POP3 instead of IMAP? If any of the following scenarios are true, POP3 could be used instead of IMAP: 1) There is a specific business reason (security or privacy concern) not to store messages on the server, 2) Each of your users accesses their messages from a single client/device, or 3) Server storage is limited.

Greatmail email hosting accounts are compatible with both POP3 and IMAP protocols. We generally recommend IMAP configurations for users accessing their mail from multiple machines or groups who use one mailbox for a specific task (for example, a support or sales group). However, if users are working from single computers and only use webmail to occasionally access new or recent mail, then POP3 can be adequate.

It should also be noted that when combined with tools that synchronize contacts, calendars, notes and tasks between the server and client, IMAP plays an important role in emulating an Exchange-like email experience.