Using digital signatures for email with Apple Mail and Outlook for OS X

You can use S/MIME certificates, also called "S/MIME Certs" or "Personal Certificates", with most email clients to digitally sign and/or encrypt email messages. At Indiana University, S/MIME certificates are provided by the InCommon Certificate Service. For instructions on getting a certificate, see Getting an S/MIME certificate for digital email signatures at IU.

When you receive your certificate from InCommon, it will be encrypted in the PKCS 12 format (.p12 or .pfx), using the strong passphrase ("PIN") you created for it at the time of request. You will need this passphrase to install the certificate.

Also, for details about potential issues with various devices and applications when using digital signatures, be sure to refer to Known issues with digitally signed email at IU.

On this page:


Installing in OS X

  1. Double-click the file downloaded from the InCommon Certificate Manager.
  2. OS X Keychain Access will prompt you for the certificate passphrase; use the second, "PIN" passphrase, not the first "request" passphrase.

The certificate will be installed on your Mac and will appear in the "My Certificates" section of Keychain Access. The certificate is now available for Apple Mail, Outlook, and other applications that can use client certificates.

Note:
Your certificate is only available on the computer and user account where you install it. If you want your personal certificate on other computers or devices, you will need to import it on those devices also.

Using your certificate with Apple Mail

Use these instructions to enable Apple Mail to use client certificates to digitally sign and encrypt email.

Enabling digital signing and encryption

  1. If you have just installed your certificate on your Mac, close Mail and then restart it.
  2. Begin composing an email message. You should see the "Signed" icon (The 'Signed' icon indicates your message will be digitally signed.) in the lower right of the message header (this indicates the message will be signed). If you don't see the "Signed" icon, select Customize (in the lower left of the message header), and add the "Lock" and "Signed" icons.

Signing email

To send a signed message, verify that the "Signed" icon has a checkmark () in it . If the "Signed" icon has an x instead, your message will not be signed.

You may not want to sign messages to mailing lists, because S/MIME digital signatures are attachments, which some lists do not accept.

Encrypting email

If you have the public certificate for the user or users to whom the messages is addressed, you will be able to encrypt the email message: In the lower right of the message header, click the open lock icon to lock it; when the icon is locked, your email message will be encrypted.

If you do not have certificates for everyone to whom the message is addressed, you will be prompted to send the message unencrypted.

Using your certificate with Outlook for OS X

Use these instructions to enable Outlook to use client certificates to digitally sign and encrypt email.

Enabling digital signing and encryption

  1. If you have just installed your certificate on your Mac, close Outlook and then restart it.
  2. From the Outlook menu, select Preferences > Accounts. Select your IU email account, click Advanced, and then select the Security tab.
  3. In the "Digital signing" section, select your certificate from the drop-down menu.
  4. For "Signing algorithm", the default value of SHA-256 is appropriate for most situations.
  5. For the best usability, enable the following options:
    • Sign outgoing messages
    • Send digitally signed messages as clear text
    • Include my certificates in signed messages
  6. In the "Encryption" section, select your certificate from the drop-down menu.
  7. For "Encryption algorithm", ASE-256 is the best option. It is not necessary to check Encrypt outgoing messages; each email message can be optionally encrypted when you compose it.
  8. IU does not currently use the "Certificate authentication" options, so do not set this.
  9. Click OK to save your changes and exit Outlook Preferences.

Signing email

By default, your email messages will be digitally signed. To indicate signing, a lock icon with the text "This message will be digitally signed" will appear in the lower left of the message header when you compose an email message:

The lock icon signifies your message will be digitally signed

If you do not want to sign a message, from the Options tab of the mail message, select Security and uncheck Digitally Sign Message.

You may not want to sign messages to mailing lists, because S/MIME digital signatures are attachments, which some lists do not accept.

Encrypting email

Address and compose your email message. From the Options tab of the mail message, select Security and check Encrypt Message.

If Outlook is unable to find certificates for everyone to whom the message is addressed, you will be prompted to search the IU Active Directory for user certificates. If Outlook is still unable to find certificates for all addressees, you will be prompted to send the message unencrypted.

Using a group account certificate

To use an S/MIME certificate with a group account, install and enable the certificate as you would for a standard account.

Notes:
  • If the profile you are using in your email client is the group account, there should be no issues.
  • If the profile you are using in your email client is your personal account and you want to send email from the group account, in your email message, open the "From" field and enter the group account address. If your personal account has "send as" rights for the group account, there should be no issues. If you are unsure whether you have "send as" rights, contact your IT Pro.

This is document bcsn in the Knowledge Base.
Last modified on 2017-10-02 14:29:12.

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