Google is adding security warnings to Gmail to help protect users from phishing and other security threats.
The change will apply to both web and Android usage, and sees Google attempt to authenticate a sender; if it can't, you'll see a question mark in place of the sender's profile photo, corporate logo, or avatar.
If you receive a message with a link to a dangerous site known for phishing, malware, and Unwanted Software, you’ll begin to see warnings when you click on the link. This will inform you that visiting this site could harm your computer. It's essentially an extension of the Safe Browsing protection available to various web browsers today.
Google notes that not all affected e-mail will necessarily be dangerous, but it wants people to be extra careful about replying to, or clicking on links in messages that you’re not sure about.