Email header analyzer
Paste the raw headers from a message you received. You'll get the delivery path, where it was delayed, and — the part other tools skip — why DMARC passed or failed even when SPF and DKIM look fine.
Nothing is uploaded. Headers contain recipient addresses, subject lines and internal hostnames, so this runs entirely in your browser. You can disconnect from the network and it still works.
Where to find raw headers
- Gmail
- Open the message → ⋮ → Show original → Copy to clipboard.
- Outlook / Microsoft 365
- Open the message → … → View → View message details.
- Apple Mail
- View → Message → All Headers (⇧⌘H).
- Thunderbird
- View → Message Source (⌘U / Ctrl+U).
Use a message you received, not one from your Sent folder. The authentication verdict is added by the receiving server, so a sent copy has nothing to analyse.
If SPF and DKIM pass but DMARC fails
That is alignment, and it is the most common reason a domain with a perfectly valid SPF record still fails DMARC.This guide explains it, with the same header block you are about to paste.