This detection rule identifies instances of email spoofing related to SPF (Sender Policy Framework) temporary errors. Attackers can exploit domains without valid MX (Mail Exchange) or SPF records, leading to DNS resolution timeouts. Depending on the email provider, this behavior impacts how such emails are treated: Microsoft Office 365 flags them as spam (fail closed), while Gmail may allow them into the inbox (fail open), albeit marked with a red padlock. The rule specifically triggers on email headers indicating a temporary SPF error during DNS lookup, which is characterized by the presence of the string 'spf=temperror' in the 'Received-SPF' header. This rule can be reproduced by sending an email from a domain that does not have an MX or SPF record set up, exemplified by the provided command using the mail utility on Ubuntu. The email's metadata and headers are analyzed to detect such behaviors for proactive fraud prevention.