Self host with own domain question

[whisperdancer]

This is not a bug, but an issue. I self host 4.6.5 with my own domain. I use a 3rd party SMTP service since port 25 is now allowed on AWS. My SMTP provider recently sent an email alerting me to suspicious possible spam activity on my account. I noticed in my activity 8 emails with

subject: Important: your Social Security Number was found on the Dark Web
All the emails were sent to eiudngfnwkwbzcnkzlzymxqxysbfcnybleflncnxltcuivf@my-domain and they SMTP provider flagged them as spam and rejected them. It appears as though a bad actor is trying to send spam using my domain and has generated a random string on the left side. I could risk losing my SMTP provider if this continues. How can I prevent this?

Am I correct in assuming my simplelogin app would ignore these since there is no matching alias for this domain?

Thanks so much.