Yes, but that's probably something most people won't do (with the prevalence of HTML email and no plaintext alternative). Also, it was a reply to the parent who

Yes, but that's probably something most people won't do (with the prevalence of HTML email and no plaintext alternative). Also, it was a reply to the parent who stated "If you disable remote content, it can't be exploited on thunderbird". Ruling out the presence of an exfiltration channel is hard. It's better to prevent rendering of messages with invalid authentication code in the first place (and not rendering it and showing a warning).