Use digital signatures for email with Apple Mail and Outlook for macOS

• Before you begin
• Install in macOS
• Use your certificate with Apple Mail
• Use your certificate with Outlook for macOS
• Use a group account certificate

Before you begin

View a video about using digital signatures in Apple Mail and Outlook for macOS.

Install in macOS

1. Double-click the file downloaded from the InCommon Certificate Manager.
2. 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.

Use your certificate with Apple Mail

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

Enable 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 () 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.

Sign 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.

Encrypt 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.

Use your certificate with Outlook for macOS

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

Enable 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. If you are using the classic Outlook interface, click Advanced, and then select the Security tab. If you are using New Outlook, click Security.
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. This section will not be available in the New Outlook interface.
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. It is not necessary to check Encrypt outgoing messages; each email message can be optionally encrypted when you compose it. If you are using the classic Outlook interface, AES 256 is the best encryption algorithm.
8. IU does not currently use the "Certificate authentication" options; if this is an option, do not set this.
9. Click OK to save your changes and exit Outlook Preferences.

Sign 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 when you compose an email message:

If you do not want to sign a message, from the Options tab of the mail message, click Sign so that it is not selected. If you don't see the Options tab, you may need to open the message you're composing in its own window. Click the far right icon next to the "From:" field.

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

Encrypt email

Address and compose your email message. From the Options tab of the mail message, click Encrypt so that it is selected. If you don't see the Options tab, you may need to open the message you're composing in its own window. Click the far right icon next to the "From:" field.

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