If email is being sent to your contacts without your having done so, and you find messages in your “Sent Mail” folder that you did not send, your email account has most likely been hacked or compromised.
You’re minding your own business, and one day you get a message from someone you’ve never heard of, asking you to stop sending them email. Worse, they’re angry about it or they accuse you of trying to send them malware!
But you don’t know them, you’ve never heard of them, and you know you’ve never sent them email.
Welcome to the world of email malware, where you can get blamed for someone else’s infection. And there’s worse news to come.
If you find your account has been compromised.
Before I get to that, there is a small possibility your email account has been compromised. The solution there is quite simple: change your password immediately, password compromises can occur due to a local malware infection or a weak password being guessed. You need to make sure all devices using these accounts are malware free before updating your email passwords.
Assuming you choose a strong password, that should prevent someone from continuing to use your account for malicious purposes.