When possible, Gmail protects your info by automatically encrypting your emails, which turns them into a code during delivery. This security tool is called Transport Layer Security (TLS) and helps prevent others from reading your emails.
Check messages
If you're on a computer or an Android device, emails that aren't protected by this security tool will show No TLS 
The No TLS open lock only appears for:
- Gmail consumer accounts (gmail.com)
- Enterprise subscriptions with hosted S/MIME enabled
Messages you're sending
- On your Android phone or tablet, open the Gmail app
.
- At the bottom right, tap
Compose.
- In the "To," "Cc," or "Bcc" field, enter your recipient's email address.
- On the right of the "Subject" field, look for No TLS
.
.Important: If you see the icon, the message might not be protected by encryption. Don’t send confidential documents, like tax forms or contracts, to that address.
Messages you've received
- On your Android phone or tablet, open the Gmail app
- Tap a message.
- Under the sender's name, look for No TLS
Important: If you see the icon, the message might not be protected by encryption.
Why some emails might not be encrypted
For this security tool to work, the email providers of both the sender and the recipient always have to use TLS. Learn more about email delivery with TLS.
"No TLS" warning on messages I reply toSome email providers send messages to Gmail addresses using TLS but can't receive encrypted messages.
If you reply to these messages, this icon could show up even though you're sending from Gmail.
Sometimes you'll get a "No TLS" warning even if a message is protected by encryption, like when:
- Encryption hasn't worked for a certain email provider in the past
- Gmail isn't directly sending the message. For example, this icon might show up if you've set up a custom domain name, such as name@yourdomain.com.