Many email providers don’t encrypt messages while they’re in transit. When you send or receive emails with one of these providers, your messages are as open to snoopers as a postcard in the mail. A growing number of email providers are working to change that by encrypting messages sent to and from their services using Transport Layer Security (TLS). Generally speaking, use of encryption in transit continues to increase over time, as more providers enable and maintain their support. Factors such as varying volumes of email may explain other fluctuations in these encryption statistics.

Below is the percentage of emails encrypted for the top domains in terms of volume of email to and from Gmail, in alphabetical order.

If you mail a letter to your friend, you’re hoping that she’ll be the only person who reads it. But a lot could happen to that letter on its way from you to her, and there may be prying eyes who try to read it. That’s why we send important messages in sealed envelopes rather than on the back of postcards. Sending and receiving email works in a similar way. But when you send or receive messages with an email provider who doesn't transmit messages via a secure connection, your emails could be open to snooping.