You have received several emails that appear to be responses from emails originally sent by you. You did not send these emails. The responders are friends of yours and do not seem malicious. What term best describes this situation?
Most likely your email has been compromised or hijacked. Malicious actors often compromise or purchase compromised emails so they can send links to viruses or phishing websites to that email's contact list. Because the emails come from a real account they are often trusted by the recipients, leading them to click links that ask them for usernames, passwords or to download some malicious application.