Paste a message's headers to see its route, delays and authentication.
A message header is the delivery record: each server it passed through, when, and what the receiving server concluded about whether it was genuine. It is where you look when mail is slow, lands in spam, or might be forged.
Paste the full header and this tool lays out the route with the delay at each hop, the SPF, DKIM and DMARC verdicts, and flags mismatches such as a display name showing a different address or replies directed to another domain. It analyses the text only. Nothing in it is looked up, and nothing is stored.
In Gmail open the message, choose the three dots and Show original. In Outlook open the message, then File, Properties and Internet headers. In Apple Mail use View, Message, All Headers.
Everything the sender's side wrote can be. The Received lines added by your own mail provider, and its Authentication-Results, are the ones to rely on, which is why they are at the top.
No. It is analysed in memory for the response and discarded. It is not logged, saved, or sent anywhere.