How can I block email spam?

Well, first, the answer is you cannot block all email spam, which is about 40% of all emails sent. There are some steps you can do to mitigate email spam, however.

Effective vs ineffective email blocking

Ineffective: Apple devices have an option to block email addresses. The primary use of this feature is to block messages from people you know or have known in the past. This feature is NOT intended to block email spam, because email spam is sent by bots that use a different email address with every mailing. Thus, if you block a spam email it will just use up another of your 3,000 entry table of blocked addresses, and you will continue getting the same spam from a different email address.

More Effective: So what should you do about all-pervasive spam email messages? The best answer is to report them as spam or junk by clicking the Junk button in the Mail app or move the email to the email account's Junk folder. When you do this the message is analyzed, and future messages with the same sender or similar content will automatically be treated as spam. You may notice that your Junk folder has messages that you did not specifically block; the mail app can also analyze messages that others have reported as spam or junk, or that have inconsistent metadata (that is, the internal header content). BUT, it may also contain legitimate messages that were misclassified as spam; this is called a False Positive, and it means that you should review messages in the Junk folder before deleting them.

Unwanted mail from legitimate businesses: While you can block the sender’s address, the better solution is to use the legally required (in some locations) Unsubscribe button at the bottom of the mail, or if you have an account with that business you should have a preferences setting for communications to manage your delivery preferences. In addition when Apple recognizes the message as coming from a list it will place an Unsubscribe button at the top of the message.

Unwanted political mail messages: While there is an unsubscribe button on messages with political content, the sender of such messages can choose to ignore an unsubscribe request.

Phishing messages: You may receive messages that say your device has a virus, or you owe money to a government, or that your account has been suspended and you have to click/tap or call a number to resolve the problem. NEVER RESPOND TO SUCH A MESSAGE. If you are uncertain contact the supposed sender using their direct phone number or website. In addition, click or tap the Forward button and send the message to reportphishing@apple.com. This lets Apple trace the source and disable their site. (On a Mac, Right click on the message or click on Message in the menu bar and choose Forward As Attachment; this preserves all of the message headers to further help Apple track the sender.)

Then mark the message as Junk.

Here is additional Apple support information about phishing:

• Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support
• Identify legitimate emails from the App Store or iTunes Store - Apple Support

One last note: When you block by any method the message does not vanish into thin air; instead it gets diverted to your trash or junk folder.