If you see a question mark next to the sender's name, the message isn't authenticated. When an email isn't authenticated, that means Gmail doesn't know if the message is coming from the person who appears to be sending it. If you see this, be careful about replying or downloading any attachments.
Check if a message is authenticated
Important: Messages that aren't authenticated aren't necessarily spam. Sometimes authentication doesn't work for real organizations who send mail to big groups, like messages sent to mailing lists.
- On your Android phone or tablet, open the Gmail app
.
- Open an email.
- Tap View details
View security details.
- The message is authenticated if you see:
- "Mailed by" header with the domain name, like google.com.
- "Signed by" header with the sending domain.
The message isn't authenticated if you see a question mark next to the sender's name. If you see this, be careful about replying or downloading any attachments.
Emails can be authenticated using SPF or DKIM.
SPF specifies which hosts are allowed to send messages from a given domain by creating an SPF record.
DKIM allows the sender to electronically sign legitimate emails in a way that can be verified by recipients using a public-key.
ARC checks the previous authentication status of forwarded messages. If a forwarded message passes SPF or DKIM authentication, but ARC shows it previously failed authentication, Gmail treats the message as unauthenticated.
Fix messages that aren't authenticated
Important:
- Do not use the DKIM length tag (l=) in message headers. This tag makes messages vulnerable to spoofing.
- If a message you sent arrived with a question mark "?" next to your email address, the message wasn't authenticated.
Messages must be authenticated to make sure they're classified correctly. Also, unauthenticated messages are very likely to get rejected. Because spammers can also authenticate mail, authentication by itself isn't enough to guarantee your messages can be delivered.
Fix messages that aren't authenticated
Make sure messages you sent are authenticated using DKIM (preferred) or SPF.
You can use these steps to prevent your emails from being blocked by Gmail:
- Use RSA keys that are at least 1024-bits long. Emails signed with less than 1024-bit keys are considered unsigned and can easily be spoofed.
- Gmail combines user reports and other signals, with authentication information, when classifying messages. Authentication is mandatory for every mail sender to ensure that your messages are correctly classified.
- Learn how to create a policy to help control unauthenticated mail from your domain.