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    GuideComplianceRequirementsEmail Headers

    Email Headers

    How Simply Send manages List-Unsubscribe headers automatically, and how to provide your own values when needed.

    Email headers identify the sender and route the message. This page covers the unsubscribe-related headers — Simply Send sets these automatically by default. If you need to override them with your own values, you can do so at the email level.

    Required — CAN‑SPAM, CASL, GDPR

    What it is

    List-Unsubscribe and List-Unsubscribe-Post are email headers that allow recipients to unsubscribe directly from their email client — without visiting a web page. Gmail and Yahoo use these headers to render a one-click unsubscribe button next to the sender name, improving deliverability and reducing spam complaints.

    Why it's needed

    Gmail and Yahoo have required List-Unsubscribe headers for bulk senders since February 2024. Without them, email clients cannot offer one-click unsubscribe — making it harder for recipients to opt out, increasing the likelihood they mark your email as spam instead. High spam complaint rates directly damage your sender reputation and deliverability.

    How to implement

    AUsing Simply Send managed unsubscribe

    Simply Send automatically generates and injects all unsubscribe-related headers for every email. No configuration is needed on your part.

    Do not set any of the following headers — Simply Send sets them automatically:

    • List-Unsubscribe
    • List-Unsubscribe-Post
    BProviding your own unsubscribe headers

    If you want to handle unsubscribe headers yourself, you can include List-Unsubscribe and List-Unsubscribe-Post headers directly in your email. When present, these override Simply Send's defaults — your values will be used instead. Both Gmail and Yahoo require these headers for one-click unsubscribe support.

    • Set List-Unsubscribe to a unique, per-user, per-send HTTPS URL pointing to your opt-out endpoint.
    • Set List-Unsubscribe-Post to List-Unsubscribe=One-Click to enable RFC 8058 one-click unsubscribe.
    • Your endpoint must respond to a POST request with 200 OK — mail clients validate this during one-click processing.
    • Do not use a mailto: link as the primary value — some providers ignore non-HTTPS values and one-click will silently fail.

    Example Header format:

    List-Unsubscribe: <https://yourdomain.com/unsubscribe?token=1234567890>
List-Unsubscribe-Post: List-Unsubscribe=One-Click