An email was sent to some of our users and the sender appears to be one of our company’s users and he didn’t send it because it shows on our gateway filter. Emails between our company’s users are handled by exchange itself.
After checking the filter gateway the message ID = ….@filter.gateway.com
And accepted from unknown IP 18.104.22.168
Reverse DNS lookup is enable on filter gateway …
How can we prevent this from happening again?
Not to accept emails with our users emails in from field unless it was originated from the user himself.