we have received an e-mail using an alias/send as from one of our domains. The e-mail was allowed through and leads to a malicious url. We have enabled the setting in E-mail Security to reject e-mails that impersonate one of our domains:
Email that appears to come from your own domain, but originates externally
Now it wasn’t rejected but as this sender does not match our spf or dmarc we feel it should have been quarantined next. It didn’t, not as far as I can see in the logs as it only gives delivered successfully.
Sophos Support claims it is a false positive and that I should send it to Sophos Labs. I can’t do anything with such support answers.
Questions: is send as / alias from a non-domain email adress using a send as / alias of one of our e-mail domains not picked up by:
a] header anomalies?
b] spf and dmarc settings?
[edited by: Raphael Alganes at 9:11 AM (GMT -7) on 2 Jun 2023]