A step-by-step guide to installing a S/MIME certificate and setting up S/MIME on your iPhone.

S/MIME encrypted email message

What is S/MIME?

The Secure/Multipurpose Internet Mail Extensions (S/MIME) is an internet standard that allows the sender of an email to protect the confidentiality of the message by encrypting its content with the public key contained in the recipient's S/MIME certificate.

The Mail app on the recipient's iPhone can then decrypt the message with the private key installed on their device. S/MIME is supported natively by iOS and Apple's Mail app.

S/MIME allows end-to-end encryption: the sender encrypts the email in a way that it can only be decrypted in the recipient's inbox, ensuring only the intended person can read it.

The sender of a message usually also signs it with their own S/MIME certificate (private key), which allows the recipient to authenticate the sender.

Get a S/MIME Certificate

You can buy a S/MIME certificate from a Certificate Authority (CA) or through a retailer, or get one free of charge from Actalis, an Italian CA.

Certificate authorities provide S/MIME certificate bundles either as a PKCS #12 file (.p12 or .pfx) if they generated the certificate for you or as a PKCS #7 (.p7b) file if you created the private key on your own computer and submitted a Certificate Signing Request (CSR) to the CA.

Transfer the S/MIME Certificate to Your iPhone

Transfer the certificate bundle to your iPhone, for example with iCloud or Airdrop. If you got the S/MIME certificate as a .p12 or .pfx file, the private key should be encrypted with a password, so it is usually considered safe to send the certificate bundle by email.

Install the Certificate on iOS

The instructions provided here were tested with iOS 14.4. If you find that they don't work with later versions of iOS, please let us know.

Opening PKCS12 Certificate on iOS

Open the certificate file. iOS should confirm the (identity) profile was downloaded, as illustrated above.

Profiles option in iPhone General Settings

Navigate to the Settings app, select General and scroll down to the bottom. Tap Profiles, as shown on the screenshot above.

Identity Profiles in iPhone Settings

Select Identity Certificate.

Install S/MIME Identity Profile on iOS

Tap Install. Enter your iPhone passcode when asked.

iOS warning profile is not signed

iOS may warn you that the identity profile is no signed. Do not proceed if you were unexpectedly asked by someone to install a certificate they provided.

As long as you know the origin of the S/MIME certificate bundle, tap Install again to confirm.

S/MIME certificate password prompt

Enter the password associated with the S/MIME certificate bundle. If you obtained the certificate as a .p12 or .pfx bundle from a certificate authority, they must have also given you the password.

The certificate's private key was encrypted with the password, so if you lost it, you won't be able to import the certificate to iOS.

Turn On S/MIME Signing and Encryption

We're now going to set up the iPhone's Mail app to digitally sign outgoing mail with the new S/MIME identity. This will allow our email contacts with a S/MIME-compatible email software to:

  • Authenticate messages we send them
  • Automatically import our public key so they can use it in the future to send us encrypted emails.
iPhone Mail app settings

Go to the Settings app, locate Mail and tap Accounts. If you have installed multiple email accounts on the device, select the one corresponding to the S/MIME certificate.

S/MIME Sign and Encrypt by Default

Tap Advanced and enable Sign (and if needed Encrypt by Default) in the S/MIME settings.

Add the Certificate to FormSmarts

Before you can receive online form submissions by encrypted email, you need to add the certificate to FormSmarts. Sign in from your iPhone (or any device where you've installed the certificate) and create a Certificate Addition Request (Step #4 in the set up instructions).

Create a S/MIME Certificate Addition Request

Send a signed email to the long email address returned when you submitted the request. You should receive an email within seconds confirming FormSmarts imported your S/MIME certificate successfully.