Alright so I was wondering if there is a way to find out if a Java client is sending out emails (without you knowing). Like if the client sends an email, or attempts to send an email if you could intercept it or at least find out what is sending that email. Thank you.
Any good firewall should be able to tell you when an application is sending network traffic such as emails. ZoneAlarm for Windows or ufw for Linux might work for you.
You can see exactly what network traffic is going out from your computer using a tool like WireShark. This will include any emails sent.
It might not be possible for you to read the email, if it using TLS for example.