Klaviyo sent emails on my behalf that i didn't do to some email list I don't have

Hey @RBM_Adrian,

Sorry to hear you’re experience this sort of issue! Certainly not an ideal experience. 

In my experience, this is most likely the behavior that @Jessica eCommerce Badassery brought up of a potentially malicious actor spoofing your from/reply-to address as their own.

Although Klaviyo doesn’t require any confirmation that you own the specific from/reply-to address you’re using, there are typically safeguards in place from the inbox providers that addresses these sort of concerns. These safeguards include ensuring your CNAME, DKIM, and SPF records are all aligned - as described in our Understanding email authentication Help Center article. Even slight misalignments will likely cause emails to be blocked or placed in the spam filter of the recipient’s inbox. 

For added security, you could also heighten the security settings via your DNS backend to prevent future malicious actors from attempting to spoof your from/reply-to address.

As a precaution, I would also suggest changing your password and enabling multi-factor authentication if you haven’t already. Since you mentioned you weren’t able to locate the profiles of the customers who reached out in your Klaviyo account, it would mean it’s highly unlikely your account was compromised. Oftentimes there would be “fingerprints” left behind if a malicious actor did get into your account to send inappropriate content. 

When you looked into the email that these customers replied to, was it the content of the recent campaign you sent? If so, then it sounds more like a recipient forwarding your emails, rather than spoofing your from/reply-to address - similar to the experience from the Community post below:

If the content was different, then it does support the first theory that @Jessica eCommerce Badassery brought up. 

One of the main reason malicious actors spoof a brand’s from/reply-to address is an attempt to lend the email more credibility to the recipients. 

I hope this helps!

David