How can we prove an exchange sold our email?

I know you can use multiple addresses for one gmail email by adding +something before the @. For example if your mail is email@gmail.com you can use email+binance@gmail.com when you create a Binance account in order to give this mail to them. If you receive a spam email and you see to "email+binance@gmail.com" in the recipient field, Binance sold your email. But how can you prove it? You know it for sure but no one stops you from using email+binance@gmail.com on other sites.

Let's consider you want to sue them but how can you prove it that you gave the email only to them?

Disclaimer: I used Binance as an example but could be Coinbase or Kraken or Crypto.com.