What are email headers?
Raw email headers are the paper trail every message leaves behind. Every server that touches an email adds a Received: line recording its own hostname, the IP it received the message from and a timestamp. Reading those lines from bottom to top gives you the actual delivery path, from the sender's outbox to your inbox. The full journey is usually over in a few seconds, but the headers preserve every step of it permanently.
Beyond the routing information, headers also carry the authentication verdict: whether SPF, DKIM and DMARC passed or failed, which mail server software sent the message, what spam score any filters assigned, and whether the message was modified in transit. When an email lands in spam, looks suspicious or arrives with a forged sender, the headers are where you look first.
How to get the raw headers
Gmail
Open the email. Click the three-dot menu in the top right corner of the message body, then select "Show original". A new tab opens with the complete raw headers at the top. Select all the text from that section and paste it here.
Outlook and Microsoft 365
Open the email, then go to File and click Properties. The "Internet headers" box at the bottom of the window contains the full headers. Click inside the box, press Ctrl+A to select everything and copy it.
Apple Mail
Select the email in your list, then from the View menu choose Message and then All Headers. The full header block appears above the message body. You can also use the keyboard shortcut Shift+Cmd+H.
Thunderbird
Right-click the message in your list and choose View Source. The entire raw email opens in a new window, headers included. Copy everything before the first blank line.