Spam being sent through one account

Help! (Home for newbies)
1

Operating system Ubuntu Linux 22.04.3
Webmin version 2.101 Usermin version 2.001
Virtualmin version 7.8.2 Authentic theme version 21.04

Starting yesterday, I am getting hundreds of Mailer-Daemons and like bounces. This is from a domain where I used to host email, but I have moved the mail for the domain to privateemail.com, and do not have mail service turned on for the domain.

I am getting Daemons like this:

From: MAILER-DAEMON@host5.johnsimmonshypertext.com
To: root@strannik.com

And then a bounce from someone’s server, indicating that the email came from root@strannik.com

How do I close this hole? I have DMARC, etc. already set up.

Host: host5.johnsimmonshypertext.com
Domain Affected: strannik.com

2

I have turned postfix off for now until I can solve the issue.

3

look at the bounce, was the originating emails IP coming from you. It maybe someone using your email address to spam. The bounced emails gives you info on the source.
DMARC rule is set to reject so its following the rule. Not sure what you can do. Maybe setup a filter to delete emails from MAILER-DAEMON@host5.johnsimmonshypertext.com