Understand your email’s headers.
See the authentication results and delivery route recorded by the mail systems that handled your email.
Free. No account required.
Where to find email headers
Where to find headers
In Gmail, open the message’s three-dot menu and choose Show original. In Outlook on the web, open the message menu and look for View message details.
Copy the complete header section. It ends at the first blank line before the message body.
These are results reported in the pasted text. Only rely on results from your receiving mail system; copied headers can be altered.