[throwaway413]

You’re lying to yourself. You got mugged. You even said it yourself - your customers started receiving emails from his other company! The writing is on the wall.

Do you have hard proof of the email your customer received?

[ganeshkrishnan]

Probably. Also remember that if posters space is specific or niche, clients usually look for other software to help them. The emails from the competitors are not a smoking gun proof. There is no way to prove or disprove it and only the investor knows what's up