Gmail: Open the email, click the three dots (More) > Show original.
Outlook: Double-click the email > File > Properties, then look under Internet headers.
Yahoo: Open the email, click More > View Raw Message.
Apple Mail: Open the email, go to View > Message > Raw Source.

Each "Received" line is added by a mail server as the email passes through it. The topmost Received header is added by the final server (recipient's), and the bottommost is from the original sender. By reading them in reverse order you can trace the exact delivery path.

SPF (Sender Policy Framework) checks that the sending server's IP is authorized to send emails for the domain. A "pass" result means the IP is allowed; "fail" often leads to spam filtering.

DKIM (DomainKeys Identified Mail) adds a digital signature to the email, verifying that the message hasn't been modified and truly comes from the claimed domain. It helps prevent email spoofing.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM. It tells receiving servers what to do if authentication fails (reject/quarantine/none) and provides reporting on who is sending emails from your domain.

Common reasons include missing or failed SPF/DKIM/DMARC, blacklisted IP, unusual sending patterns, or content that triggers spam filters. Use this analyzer to check if authentication passed and trace the server path.