mAIb Deliverability Repair

Analyse a message

Paste the headers of a message you have sent. Most of what a domain scan cannot determine becomes a definite answer here, because the receiving system recorded what it actually saw.

Your message headers stay in this browser. They are parsed by JavaScript on your own device. Nothing is uploaded, nothing is logged, and nothing is stored.

Paste headers

Paste everything from the top of the message down to the first blank line. Including the body is harmless — it is discarded before parsing.

Where to find the headers

Gmail: open the message, use the three-dot menu, then Show original. Copy everything in the panel that appears.

Outlook on the web: open the message, three-dot menu, View, then View message source.

Outlook desktop: open the message in its own window, then File, Properties, and copy the Internet headers box.

Apple Mail: View, Message, All Headers.

Send the message to a mailbox at a different provider from the one you send from — a message that never leaves your own mail system is not checked the same way.

What the headers settle

  • Whether DKIM is actually working. The DKIM-Signature header names the signing domain and the selector, and the receiving system records whether verification succeeded.
  • Whether alignment passes. Alignment compares the From domain a recipient sees against the domain that authenticated. It is a property of a delivered message and cannot be read from DNS.
  • Whether one-click unsubscribe is present. RFC 8058 needs both List-Unsubscribe and List-Unsubscribe-Post; having only the first is the most common way this is got wrong.
  • Which system actually received it, and therefore whose rules applied.

One caution about Authentication-Results

Any system can write an Authentication-Results header. Only one added by the receiving system means anything. This analyser prefers a header stamped by a receiver it recognises, and where it cannot attribute one it says so rather than presenting the contents as verified.