Email encryption in transit

S/MIME is used to support enhanced encryption in transit, and automatically encrypts your outgoing emails if it can.

Important: These steps only work if you have S/MIME enabled on your account.

Check if a message you're sending is encrypted

  1. Start composing a message.
  2. Add recipients to the "To" field.
  3. To the right of your recipients, you'll see a lock icon that shows the level of encryption that is supported by your message's recipients. If there are multiple users with various encryption levels, the icon will show the lowest encryption status.
  4. To change your S/MIME settings or learn more about your recipient's level of encryption, click the lock, thenView details .

Check if a message you received is encrypted


  1. Open a message.
  2. On an Android device: Tap View details and thenView security details.
    On an iPhone or iPad    : Tap View details.
  3. You'll see a colored lock icon that shows you what level of encryption was used to send the message.

What the encryption icons mean

When you're sending or receiving messages, you can see the level of encryption a message has. The color of the icon will change based on the level of encryption.

I see the red lock icon

If you're writing a message and see the red lock icon, consider removing these addresses or deleting the confidential information. To see which address is unencrypted, click View Details.

If you received a message with the red lock icon and the message contained particularly sensitive content, let the sender know and they can contact their email service provider.

Learn more about encryption

Why some emails might not be encrypted

If the person you're emailing is using an email service that doesn't encrypt all messages using S/MIME or TLS, their emails might not be secure. However, messages are encrypted in S/MIME whenever possible.

For S/MIME to work, to either sign or receive S/MIME encrypted mail, a user must have a valid S/MIME cert from a trusted root.

S/MIME (enhanced encryption)

S/MIME is a long standing protocol which allows encrypted and signed messages to be sent using standard mail delivery SMTP.

It uses public key cryptography to:

  • Encrypt the message on send and decrypt the message on receipt with a suitable private key to keep message content private.
  • Sign on send and verify the signature on receipt to authenticate and protect integrity.

Note: A message can't be decrypted if the user's key isn't uploaded when the message is delivered. Learn more about uploading certificates.

TLS (standard encryption)

Opportunistic TLS (STARTTLS) is a protocol that helps provide privacy between communicating applications and their users during email delivery. When a server and client communicate, TLS ensures that no third party can overhear or tamper with any messages.

For delivery TLS to work, the email delivery services of both the sender and the receiver always have to use TLS.

Learn more about TLS email encryption.

Related resources

  • Gmail Security and Privacy Settings

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