I learned that most email services do attach the IP address of the MUA (that is, the user's computer) if you send through SMTP. I set up an SMTP relay for mysel

I learned that most email services do attach the IP address of the MUA (that is, the user's computer) if you send through SMTP. I set up an SMTP relay for myself to hide that. The user's IP address is not attached if you use webmail.