How can I configure iCloud mail in Mozilla Thunderbird?
These settings work for me, see also https://support.apple.com/HT202304.
Incoming

Protocol: IMAP
Server: imap.mail.me.com
Port: 993
SSL: SSL/TLS
Authentication: Normal password

Outgoing

Protocol: SMTP
Server: smtp.mail.me.com
Port: 587
SSL: STARTTLS
Authentication: Normal password

Username for both should just be your actual username &quot;karlo_lopez&quot;, not your whole email address.

VERY IMPORTANT NOTE:
If your Apple ID is protected with two-factor authentication, then you need to setup an app-specific password within your Apple ID account. Enter that password instead of your normal iCloud password when setting up the email address into Thunderbird.