Apple iCloud Users have the option of using two-step verification or two-factor authentication.
Existing Match My Email Users that choose to use the 2-factor authentication offered for their iCloud email accounts, may get an alert that their IMAP credential should be updated. Users actually need to create a specific app password as recommended by Apple. New Match My Email Users should also do this and then use that password when setting up Match My Email import.
1. Create app specific password
2. Login to MatchMyEmail
3. Click on Email Imports on the left. In the next panel click Import 1 or the name of the Import the Admin confirmed, and click the Pen tool to edit.
4. In password field, enter the specific app password. Click Save at bottom.