You are currently following two communities, iCloud on my Mac and Numbers for Mac, and your email preferences are set up to send email for content that you are following. You can either visit your following communities page to unfollow the communities via the gear icon or check your account's preferences page and change the email settings so that you no longer get emails for Content I'm following. You can set the other options to suit your taste.

Use the first option if you want to continue to receive emails for replies to your own questions. You can also visit this following content list to unsubscribe from individual threads via the gear icons there.
If you want to disable all email you can check for replies to earlier questions using this following discussions link which you could bookmark. It will highlight any threads with new activity since you last viewed them.
If Content I'm following is already off, and you're still receiving emails, try turning it on, save the change then turn it off and save again.
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