Enabling Client Certificates for iOS Mail

Enabling these options will allow you to digitally sign  and encrypt all email sent from your device.

  1. Go to Settings > Mail, Contacts, Calendars.

  2. Select the email account associated with your Client Certificate.

  3. Tap the Account button with your email address.

  4. On the Account screen, change the "S/MIME" setting to ON. The "Sign" and "Encrypt" options are off by default.

    • To enable signing, tap Sign, and then select your certificate. This will digitally sign every email you send from your email account on this device.

    • To enable encryption, tap Encrypt, and then select your certificate.

      The encryption option will attempt to encrypt all correspondence from your iOS device. If you do not have the public certificate for a recipient, the email message will not be encrypted.

You also read Apple's knowledge-base article related to this here: