I only know the person's email, but I need more information about him. How can I find more information on the Internet? Who knows what services can help me?

Today, knowing a person's email address is enough. A lot of services can gather information based on that data alone. You'd be surprised how much data you can get. Read the article https://celltrackingapps.com/10-best-free-reverse-email-lookup-services/ about these services. You might find this information useful. I have used several such services and have been very satisfied. I don't see anything wrong with using the benefits of civilization for personal purposes.