Thunderbird setup

These screenshots show the correct setup for Thunderbird.

It is easiest to add a new account and then modify the settings so that SSL or TLS is enabled, as shown.  The server will refuse any insecure connections.

Receiving mail: IMAP

Thunderbird IMAP setup

Thunderbird IMAP setup

Receiving mail: POP3

Thunderbird POP3 settings

Thunderbird POP3 setup

Sending mail

Thunderbird SMTP setup