• Correct setup of the email client Outlook for Mac 2019
• Correct integration of the Certification authorities into the operating system.
• Valid digital User certificate integrated into the operating system.

• Start Microsoft Outlook for Mac 2019
• Tools → Accounts…
• <your email account> → Advanced…
• Card Security
  • Digitally sign:
    • Certificate: select your digital user certificate here.
    • Signature algorithm: SHA-256
    • Sign outgoing messages: enabled
    • Send digitally signed messages as plain text: enabled (default)
    • Include my certificates in signed messages: enabled (default)
  • Encryption:
    • Certificate: select your digital user certificate here.
    • Encryption algorithm: AES-256
    • Encrypt outgoing messages: disabled
  • Certificate authentication:
    • Client certificate: No selection (default).

The configuration is now complete and you can sign any e-mail. If you have the public key of your communication partner, you can also encrypt every e-mail.

• In Microsoft Outlook for Mac 2019, click the New Email icon and compose.
• Before sending, check that the message is digitally signed in the “Options” menu.
• As soon as you click on “Send”, the email is digitally signed and then sent.
  • You may be asked to enter your local user name and password once more.
• The communication partner will see the loop symbol as a sign of a digitally signed e-mail.

To encrypt, you must first have the communication partner's public key. To do this, have your communication partner send you a digitally signed e-mail, for example, which will automatically be added to your key ring.

• Click on the “New email” icon in Microsoft Outlook for Mac 2019 and compose it.
• Before sending, check that the message is encrypted in the “Options” menu.
• As soon as you click on “Send”, the email is encrypted and then sent.
  • You may be asked to enter your local user name and password once more.
• The communication partner sees the lock symbol as a sign of an encrypted e-mail.