There is a feature called “Captcha” in the Email Form block that should usually be enabled. It helps to detect bots and spammer tools and stops them from sending spam messages to you using your own email form.
The Captcha box has been made simpler and much of the “extra stuff (noise)” has been removed from its display. Therefore, it is now easier to understand for users.
In addition, this Captcha feature is now enabled by default. (Previously, it was off by default)
If you had previously disabled this feature, you should edit your Email Form blocks and enable it. This is a very helpful feature.
You can read more about the Captcha feature here.