So we have a pretty decent spam filter. The problem now seems to be that someone out there is impersonating one of our e-mail addresses, and is sending out spam claiming to be us. Our mail server then floods one of our executives (email@example.com)
with a ton of bounce-back message.
I don't know how they're doing this, all our SPF records are up and I'm passing all the tests at mxtoolbox.com. Any ideas where I can go to troubleshoot? I'm including one of the bounce-backs... domain.com is an alias for our own domain.
Delivery has failed to these recipients or groups:
The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk.
The following organization rejected your message: mxs.mail.ru (18.104.22.168).
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