Maybe they are thinking of headers such as: From, Original-From, and Resent-From. IANA list of email headers: https://www.iana.org/assignments/message-headers/

Maybe they are thinking of headers such as: From, Original-From, and Resent-From. IANA list of email headers: https://www.iana.org/assignments/message-headers/message-headers.xhtml https://www.iana.org/assignments/message-headers/message-hea...