A friend of mine is hosting his site on a shared hosting.
All was good, until yesterday when he got maybe 200 emails saying:
"A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:..."
The problem is he never sent these emails!!
The return addresses are to addresses he never created like: mike@websiteName.com, charlie_bean@websiteName.com, etc. I substituted the real domain name with "websitename.com" to keep the website secret for now.
He never sent emails under these nonexistent email addresses.
I can only think of 3 possibilities, but It would appreciate your help in figuring exactly where the problem lies:
One is spamming a whole lot of people with a return address as firstname.lastname@example.org. And he's constantly changing the first part of the return email address. He is using his own server, but use the return address to confuse people on who is sending the email address. Is that possible?
The hosting email server has been hacked.
Her computer has been hacked, although I doubt that. He said to me that he's not able to send emails using outlook for some time. If his outlook was not configured properly, then a virus or a malware wouldn't be able to send emails either.
How can I resolve that issue as these error messages are jamming his inbox.