This guide explains how to switch from a POP configuration to an IMAP configuration for the same email account in your email software/client. Indeed, for many reasons, it is strongly recommended to use the IMAP protocol instead of POP.

Switching from the POP protocol to the IMAP protocol…

If your email address is already configured with the POP protocol in your email software/client (Mozilla Thunderbird, Microsoft Outlook, etc.), it is not possible to switch to the IMAP protocol directly on the account. Indeed, most common email software/clients do not allow you to modify an existing POP3 account and define it as IMAP instead.

The solution is therefore toadd the same email account but using the IMAP protocolin your email software/client, then move your messages and folders from the POP account (on your computer) to the IMAP account (on the email server).

… with Microsoft Outlook

Some versions of Outlook, such as 2016, prevent you from easily adding a second account with the same name (identical email address).

To work around this, you need to add the account from the Profiles section:

From there, you can add the additional account using IMAP:

1. Configure the new email account using the IMAP protocol (the same account as the one configured in POP, but this time in IMAP):
   
2. Move one folder at a time by dragging it to the inbox of the new account configured in IMAP:
   
3. Wait for the transfer to complete (this may take some time depending on the amount of data being transferred to the server); the progress is indicated at the bottom of the window:
   
   

If your POP account kept a copy of the messages on the server (an option that is not recommended and can be found in the advanced settings of your Outlook), you may end up with duplicate messages.

… with Apple Mail

Deleting a mail account configured in POP deletes the messages it contains. It is therefore recommended to disable the POP account instead of deleting it!

Once the POP account is disabled, refer to this other guide to configure your email address in Apple Mail, using IMAP.

Once you are finished, all that will remain is to drag the messages from your POP account's folder structure to the new IMAP account's folder structure.