Outlook S/MIME Digital Signature Warning


User sees this message at the top of an email in the Outlook Web app:

"This message has a digital signature, but it wasn't verified because the S/MIME control isn't currently supported for your browser or platform"


Managed MacOS Computer


  • The user was sent an email with an attachment and a self-signed digital signature, but the Outlook web app was throwing an error in both Chrome and Safari due to that signature.
  • The attachment was able to be opened in the Outlook desktop app.


  • The S/MIME error refers to a protocol that only works on web clients when on Windows devices.
  • It works on Mac desktop apps (Outlook for example), but the Outlook Web app for Mac devices does not support the protocol.
    • That is why the error is visible on both Chrome and Safari, but not on the Outlook desktop app.

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Article ID: 140714
Mon 3/18/24 8:58 AM
Fri 3/29/24 2:01 PM