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POP3 or IMAP email
This guide explains the differences between the IMAP and POP3 connection protocols from a mail client (Outlook, Microsoft 365, Thunderbird, Apple Mail, eM Client, etc.) and why you should never use them at the same time.
IMAP/IMAP4 advantages
With IMAP, emails stay on the server and are therefore accessible from any computer connected to the Internet, via Mail the Infomaniak mail interface or Infomaniak Mail the smartphone app.
This is practical if your connection is permanent, if you want to access all your messages from multiple locations simultaneously (at home, on the go, on vacation, etc.), and if multiple users share a service mailbox from different workstations.
You will always have the same view of the messages on the server, everyone will see the same messages: if a message is deleted by one 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
In principle, you need to be connected to the Internet to view messages (but some mail clients, or email clients, on some mobile devices will allow you to display the inbox even without a 4G/5G or Wifi connection).
POP/POP3 advantages
Emails are removed from the server and sent to the computer. They are therefore accessible even when you are offline. This is practical if your connection is expensive or not permanent, or to keep a local version if you cancel your email provider subscription.
Disadvantages
Emails no longer appear on Mail. You cannot have multiple people accessing the same mailbox because the messages are deleted each time you access them, so you will have the impression of missing or seeing some messages disappear. In addition, if you "keep a copy of the messages on the server" (an option in the email client), the more double-saved emails you have, the greater the risk of encountering problems (see below).
Never mix POP and IMAP
Since the IMAP protocol is not compatible with the POP3 protocol, you should not try to connect to Mail (IMAP) when a mail client configured in POP3 is used for the same address being consulted.
It may happen that your email client, 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 "keep a copy of the messages on the server" option.
This configuration can work perfectly for a while, but then problems can occur, such as the re-download of messages.
To avoid this, we strongly recommend using the IMAP protocol. We direct you to this guide which explains how to configure an account in IMAP and this guide to switch an existing account from POP to IMAP.
If you still want to use the POP3 protocol avoid enabling the option to keep a copy of the messages on the server.