Hi Neoma!

Junk mail is unfortunately inevitable. What you can do is train your spam filter in your webmail and also in Thunderbird, so new spam can be classified more effectively. This article has information about this: Thunderbird and Junk / Spam Messages. iCloud should have their own documentation about this.

Regards, Balázs

You can adjust your iCloud Mail settings to filter out junk more effectively. Go to iCloud.com, open Mail, and check the settings for spam filtering. Also, mark unwanted emails as junk so iCloud learns to filter them better. If you're still getting a lot, consider setting up rules to automatically delete or move emails from unknown senders. Another option is to use a third-party email filter. Hope that helps!