How To: View an Email Header

In short. Clients hide the technical trail. You need the original / internet headers, not the From chip. Most mobile apps do not expose them.

Gmail

• Open the message on the web.
• Next to Reply, ⋯ → Show original.
• A new tab lists the full source. Gmail summarises SPF, DKIM and DMARC at the top — still read the raw Authentication-Results line.
• The Gmail app has no Show original. Use a desktop browser, or request the desktop site.

Outlook

• New Outlook / Outlook on the web — ⋯ → View → View message details. Copy the internet headers.
• Classic Outlook for Windows — double-click to open the message window (the reading pane is not enough). File → Properties → Internet headers.
• Outlook for Mac — View → Message → All Headers.

Apple Mail

• Mac — View → Message → All Headers (Shift+Cmd+H), or Raw Source (Opt+Cmd+U).
• All Headers is a global toggle. Switch back to Default Headers when you are done.
• iOS Mail — no native header view. Use a Mac, or forward the message as an attachment to a desktop.

Yahoo Mail

• Open the message, ⋯ → View Raw Message.
• Headers end at the first blank line.

In the simulator

• Use Email headers on any message.
• Turn on Auto-format headers if the block is one long line.

Do not paste live incident headers into random analyser websites. Prefer your IT team, or for Gmail Google’s Messageheader tool. Then read which fields to trust.