<title> is not an allowed tag, so nh3 unwrapped it and kept its text — "mailer", "Email template" or the subject rendered before the content. It is now dropped with its content, both in the sanitized HTML and in the text derived from HTML-only mail (snippet and search). SANITIZER_VERSION goes to 4 so stored bodies re-sanitize from the raw blob on next render. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>