If you get so many unwanted email from your website contact form, possibly most of them are coming from robots. You can install Recaptcha Version 2 or Version 3 on your website to prevent spam email from your website. This will reduce the number of unwanted email coming from any WordPress Website.
Installing the Recaptcha Version 2 will add "I'm not a robot" verification system on your website. Before anyone send an email to you, they need to pass the human verification. Also, you can add similar system on your website comment box. This will help you to prevent unwanted activity on your website.
How to Add I'm Not a Robot Verification on WordPress Contact Form 7?
You can easily add I'm not a robot verification method on your WordPress website using a simple plugins Contact Form 7 Recaptcha. To activate the security system, you just need a Secret Key and a Security Key. Adding the recaptcha system will help you to prevent suspicious activity on your website. No, robots will able to send any email through the website contact form.