This week, Google is pushing the slightest of changes to their web and Android Gmail apps that should help inform you of potential risks ahead when accessing individual emails. Going forward, as emails flood into your inbox that can’t be authenticated by Google, they’ll replace the avatar of the sender with a big red question mark (see above).
That question mark should stand as a warning that the email may be unsafe, is from an untrusted source you may not want to reply to, and could potentially contain dangerous links or attachments. Taking that a step further, if you are accessing Gmail from the web and an email comes through with a potentially dangerous link embedded, Google will start warning you before you ever get to the destination that it may be unsafe.
These changes are set for a gradual rollout and could take weeks before we all see them.
Via: Google Apps Updates