Why Your Email Headers Are Secretly Tanking Your Outlook Deliverability

Most teams focus on SPF, DKIM, and DMARC but forget about the email headers — the invisible signals Outlook watches closely.

Headers like Precedence or List-Unsubscribe can mark your email as marketing or bulk mail even when it’s transactional. For example, setting “Precedence: bulk” is a red flag for Outlook’s filters.

Also, including mailing-list tags or redirecting unsubscribe links through third parties makes your message look suspicious. Outlook prefers a simple, direct unsubscribe header that matches your domain.

Lemon Email crafts headers carefully to reflect transactional intent. We remove “bulk” signals and use “Auto-Submitted: auto-generated” to show it’s a one-off, system-triggered message.

These subtle tweaks keep your emails out of junk folders because Outlook’s filters read headers as carefully as your users read subject lines.

If your headers are sloppy or generic, no amount of SPF or DKIM will save you from Outlook’s spam folder.