In a strict sense, bounces sent with a non-empty codice_1 are incorrect. RFC 3834 offers some heuristics to identify incorrect bounces based on the local part (left hand side before the "@") of the address in a non-empty codice_1, and it even defines a mail header field, codice_11, to identify auto replies. But the mail header is a part of the mail data (SMTP command codice_12), and MTAs typically don't look "into" the mail. They deal with the "envelope", that includes the codice_4 address (a.k.a. codice_1, codice_15, or "reverse path") but not, e.g., the RFC 2822-codice_16 in the mail header field codice_16. These details are important for schemes like BATV.