We recently received a bunch of emails like the following:
From: Mail Delivery System <MAILER-DAEMON@guardedhost.com> Sent: Thursday, March 4, 2021, 7:55 PM Subject: Undelivered Mail Returned to Sender. This is an automated message from the mail system. I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below. The reason for delivery failure is included in the message below. <firstname.lastname@example.org>: host mx-ha02.web.de[184.108.40.206] said: 550 Requested action not taken: mailbox unavailable (in reply to RCPT TO command)
Apparently, guardedhost.com is owned by crooks who send these emails to millions of people, and probably 1-2% of the people click on the attachment. It is not clear what the benefit is to the guardedhost.com people, but they may collect statistics on people who are not savvy and then scam them seriously later.