How to stop or filter spam in Mac Mail

Please note that this option is only effective if you have all of your contacts in your computer's address book.
Click on below link for information on adding contacts to your address book:
Adding contacts to Mac address book

This method of filtering spam will:
1. Put all emails from the known senders / contacts in your Inbox.
2. Put the emails from unknown senders into your Junk folder.

Adding contact to your Mac address book:
1. Open Mac Mail
2. Click on Mail > Preferences and then
3. Click on Rules icon (upper left corner)
4. Click on Add Rule
5. For Description, type a name of your liking (for example Spam Rule)
6. Enter the following rule:
    - If any of the following conditions are met
    - Select Sender is not in my Address Book
    - Select Move Message to mailbox: Select Junk

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Better mailbox organization to reduce spam:

You can better manage your emails and deal with spam, if you can organize your mailboxes into three folders:

1. Known Email Addresses folder - Only receives emails from known email addresses from your email address book.
2. Unknown Email Addresses folder - Only receives emails from unknown email addresses
3. Website Inquiries folder - Only receives emails from website inquiries and orders

The unknown email address folder is going to be primarily filled with spam. You can scan through that folder quickly for any legit email.