This guide explains the differences between the IMAP and POP3 connection protocols from a software/email client (Outlook, Microsoft 365, Thunderbird, Apple Mail, eM Client, etc.) and why you should never use them at the same time with (among others) an email address managed by Infomaniak.

Advantages of IMAP / IMAP4

With IMAP, emails remain on the server and are therefore accessible from any internet-connected device via the web app **Mail** (online service mail.infomaniak.com) or the mobile app **Mail** ( application for iOS/Android smartphone or tablet).

Practical if your connection is permanent, if you want to access all your messages from multiple locations simultaneously (at home, on the go, while traveling, etc.) and if several users share a service mailbox from different workstations.

You will always have the same view of messages on the server; everyone will see the same messages: if a message is deleted by a user, the other users will no longer see that message. If it is moved to a folder on the server, all users will see that message in that folder.

Disadvantages

You generally need to be connected to the Internet to view messages (but some email clients and mobile devices will allow you to display the inbox even without a 4G/5G or WiFi connection).

Advantages of POP/POP3

Emails are removed from the server and sent to the computer. They can therefore be accessed even when offline. Useful if your connection is expensive or not permanent, or to keep a local version if you stop your subscription with the email provider.

Disadvantages

Once retrieved on a device configured with POP/POP3, emails no longer appear on the web app **Mail** (online service mail.infomaniak.com) or the mobile app **Mail** ( application for iOS/Android smartphone or tablet). You cannot have several people viewing the same mailbox because the messages are deleted with each consultation, you will have the impression of missing or seeing certain messages disappear. Moreover, if you "keep a copy of messages on the server" (option of the software/client), the more the number of double-stored emails increases, the greater the risk of encountering problems will be (read below).

Never mix POP and IMAP

It may happen that your email software, Microsoft Outlook in particular, starts to retrieve all messages, including those you have already received and read in the past.

The cause is often a POP3 incoming server configuration with the option "keep a copy of messages on the server".

This configuration can work perfectly for some time, but then issues may arise, such as messages being re-downloaded.

To avoid this, it is recommended to use the IMAP protocol: this other guide explains how to configure an IMAP account and this other guide shows the solutions to switch an existing POP account to IMAP.

If you still want to use the POP3 protocol, avoid enabling the option to keep a copy of messages on the server.