Gmail’s Mailed-by and Signed-by details help you inspect the domains involved in delivering and signing a message. They are useful evidence about email authentication, but neither field is a promise that the sender’s request, website, or attachment is safe.
Open the sender details
- Open the individual message in Gmail on a computer. In a conversation, expand the particular reply you want to inspect.
- Click the small down arrow in the sender details near the recipient line.
- Read the full sender address and the Mailed-by and Signed-by domains. Compare complete domain names rather than just a familiar brand word.
On Android, Google’s documented route is View details, then View security details. Other clients may expose authentication information through their full-header viewer instead of Gmail’s labels.
Understand what the domains establish
Mailed-by relates to the sending domain information used in mail authentication. Signed-by identifies the domain associated with a verifiable DKIM signature. A legitimate company may use a delivery provider, so different-looking domains require investigation rather than an automatic verdict.
For deeper inspection, use the message’s More menu and Show original. Gmail can show authentication results, including SPF and DKIM. A result from a trusted receiving service is more useful than an arbitrary line copied into the message body. Forwarding and mailing lists can complicate interpretation.
Use the result to choose a safe next step
If a message asks for money, a password, or a change of payment details, verify that request through the organization’s known website or an established phone number. Do this even when authentication passes: a scammer can authenticate a domain they control, and a legitimate account can be compromised.
If an expected message is unauthenticated, tell the sender through a separate channel and let their mail administrator investigate. Do not turn off Gmail’s warnings or add a broad spam exception merely because a display name looks familiar. Share full headers privately only when support needs them.
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References
Reviewed against the linked product guidance, standards, and identified vendor or public-authority guidance on October 29, 2026. Available options and screen labels can vary by account, device, region, and organization policy.