Got a question about blacklisting behaviour. Internet MX records for “mydomain.com” point to my anti-spam gateways. The anti-spam gateways then relay the email to my mail server. If someone sends an email to ,say, email@example.com the email is first accepted by the anti-spam gateway, but it will then be rejected by the downstream mail server because the recipient does not exist.
Now, my colleague says that he’s seen this behaviour result in a mail relay getting blacklisted (he gave AOL as an example). I have not seen this myself, but I’m not sure if its because I’ve been lucky or if its because he’s wrong. Can anybody clarify this?
Maybe. This is called backscatter, and some services do take it into account in computing IP reputation, and some blacklists operate exclusively based on backscatter.
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