"This message may not have been sent by..." warning
Why is this warning being shown?
The missing data can indicate one of the following:
- The message was forged and not really sent by the sender’s stated Gmail address
- The sender emailed it through a website (for example, a website sharing a news article with you)
- The message was sent by Gmail, but the authentication information was lost (for example, if you auto-forward all messages from your school email address to your personal Gmail address)
If the email wasn't sent with Gmail, but the sender includes authentication data in the message, we'll show you the sender's name and the service that authenticated the message. For example, if firstname.lastname@example.org sent you a card from a website called ecard.com, you'd see the sender listed as "email@example.com via ecard.com.”
The messages are legitimate, and I don't want these warnings to be shown
How frequently are you seeing the warning message?
Are you auto-forwarding your messages from another account?
Please contact the sender or mailing list owner to alert them. The warning is usually a sign that they're not using best practices to authenticate their emails.
What kind of address are you sending from?
How are you sending messages?