Safer Internet Day was this week and Google took action by not only giving us 2GB of free storage, but also trying to make email safer. Gmail automatically encrypts your incoming and outgoing emails with TLS encryption. This helps protect your emails as well as thwart email impersonations. However not all email services support this encryption.
From now on when you are sending an email. Gmail on the web will notify you with a little broken lock icon if they do not support TLS encryption. If you click the icon it will warn you not to send any sensitive information, as it isn’t secure. The second visual cue will come from emails you receive. Instead of the profile photo you will see a question mark.
Now just because an email doesn’t support TLS encryption doesn’t mean it’s dangerous. However it’s always best to be cautious, and it’s nice to get a little heads up from Google when you should be more skeptical.
Source: Gmail Blog