Outlook on the web offers limited support for S/MIME digital signatures

  • You cannot create digitally signed email using Outlook on the web. You may receive the following error, “An error occurred while sending this S/MIME message. The certificate used to sign this message isn’t trusted by your organization.”, when you attempt to send a message that you enable to send as digitally signed. If you need to send digitally signed emails, a desktop email application, such as Outlook, is recommended.
  • In Conversation view or the Preview pane you may not be able to read, reply to, or forward digitally signed email messages depending on which version of Outlook on the web your account is on.
    • You will see a red gum ball indicator with message: “S/MIME isn’t supported in this view. To view this message in a new window, click here.”
    • Reply, Reply All, Forward links will be unavailable or grayed out. Attachments will also be unavailable.
      • Microsoft is aware of this behavior and has stated that this is by design.
      • The UW-Madison Office 365 team has requested that this behavior be changed. Microsoft has receive our feedback and will assess the need to make this change in a future version.
  • To read, reply to, or forward digitally signed email, click the blue Click here link or by double-clicking to open the message in a popup window.
  • If you receive digitally signed emails regularly, you may find that it is more convenient to use a desktop email client, such as Outlook.

Note: view Microsoft documentation for further details.

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