Free tool
Paste the full headers (in most mail programs: "show original", "view source" or "message details"). You get the servers it passed through in order, the time spent at each, what the receiving server concluded about SPF, DKIM and DMARC, and whether the visible sender matches the technical one.
What this checks
Every server that handles a message adds a Received: line at the top, so the bottom line is the first hop and the top line the last. Each names the server it got the message from, the server that added the line, the protocol and a timestamp; the difference between consecutive timestamps is the time the message sat at that hop. Authentication-Results is added by the final receiver and records its own SPF, DKIM and DMARC verdicts. Lines below the first Received: were set by the sender and can say anything.
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Mailboxes in Luxembourg
NovaNode Mail gives you the MX, SPF, DKIM and DMARC records to copy into your DNS, with mailboxes stored in Luxembourg.