Error: "The server where you are logged on uses a certificate that cannot be verified"

This error message appears because you have set the names for the IMAP/POP/SMTP servers in the form of mail.domain.xyz and have activated the SSL option, whereas the SSL certificate is only valid for our infomaniak.com domain.

You need to use mail.infomaniak.com as the incoming and outgoing server in order to be able to use SSL for the connection.