A very simple yet decent spam filter accordingly just checks whether a message's sender is known and treats anything from untrusted sources as unwanted mail. In Mozilla Thunderbird, you can use the address book and message rules to set up such a filter.
Of course, sender filtering works best when you typically communicate with a known and closed circle of senders. You may want to turn it on only for a certain account — say, the one known to your best friends only.
Filter as Spam Mail from People Not in Your Mozilla Thunderbird Address Book
To make Mozilla Thunderbird treat all messages from senders not in your address book as spam:
- Select Tools | Message Filters... from the menu.
- Select the desired account (or Local Folders for accounts that deliver to your unified Inbox) from the Filters for: list.
- You have to create the spam filter for each account separately.
- Click New....
- Type "Unknown Sender -> Trash" under Filter name:.
- Make sure For incoming messages that: reads From isn't in my address book Personal Address Book.
- If you have more than one address book, make sure Match all of the following is selected, click + after the first criterion and add From isn't in my address book ___ criteria for all desired contact lists.
- Select Move Message to Trash, Set Junk Status to Junk or Delete Message under Perform these actions:.
- Click OK.
If you receive messages from mailing lists and do not know the individual senders in advance, set up additional filters that look for characteristic details such as a To: line and move matching emails to the Inbox, setting the junk status to Not Junk.