OWA, S/MIME on EDGE in MacOS 15.6 Sequoia

Question

OWA, S/MIME on EDGE in MacOS 15.6 Sequoia

M Mosher 1

Still receiving "This massage has a digital signature but it wasn't verified because the S/MIME control isn't currently supported for your browser or platform" when using EDGE (138.0.3351.121) after installing S/MIME (https://microsoftedge.microsoft.com/addons/detail/microsoft-smime/gamjhjfeblghkihfjdpmbpajhlpmobbp) [Version 20.25.506.1 Updated May 6, 2025 ]and adding the appropriate business domain in extension options and restarting the browser.

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3 answers

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Answer 1

M Mosher 1

Lychee,

That solution did not work. First do not have the ability to modify the business environment, I contacted them about why no one can find a fix for this when it is a requirement to use.

I can not Enable the following flags: "#enable-smime"

That flag does not exist in the browser list, I did a search from the experiments page and a text search by "CMD-F"

Lychee-Ng 27,955 Reputation points Microsoft External Staff Moderator

2025-11-19T06:39:03.5333333+00:00
Hi, Edge is currently on version 142, and a lot of flags from previous versions have been discontinued. And since you cannot modify business environment, the options are limited:

Use system native browser instead of Edge (e.g. Safari)

Use Outlook desktop client for Mac

I have to note that S/MIME in OWA on macOS browser is not supported. That extension can't fully function because it was made for Windows. So even if you install it on Edge, it won't work as expected.

You can push for more attention on this by sending Feedback to Edge (press Alt + Shift + I). In the meantime, Safari may have native S/MIME support that's suitable with Mac environment.

Answer 2

Lychee-Ng 27,955 Microsoft External Staff Moderator

Hi M Mosher,Just checking in to see if the above information was helpful. If you have any further updates on this issue, please feel free to post back. If you think my reply is helpful to you, please remember to mark it as an answer. Warm thanks.

Lychee-MSFT | Microsoft Q&A Support Specialist

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Answer 3

Hi M Mosher,

Welcome to Microsoft Q&A!

Thank you for reaching out. I totally understand and feel your frustration with the ongoing S/MIME control failure in Microsoft Edge, especially after you have already installed the extension and configured the domain settings correctly.

This happens because the S/MIME extension relies on native messaging components that are only available on Windows platforms, which macOS normally does not support. Due to that, the extension cannot fully enable S/MIME functionality in Outlook on the Web (OWA), and the error message you’re seeing is a fallback placeholder indicating that the platform is unsupported.

You can find a similar issue discussed here: SMIME Extension Error in EDGE - Microsoft Q&A with a proven solution to enable S/MIME capabilities in OWA for supported platforms.

If you're in a business environment, contact your admin/IT
Run Set-SmimeConfig (ExchangePowerShell) | Microsoft Learn
Enable the OWAIncludeSMIMECapabilitiesInMessage parameter.

Set-SmimeConfig -OWAIncludeSMIMECapabilitiesInMessage $true

There are also other options you can try if the above solution doesn't work:

1 - Fix certificate trust in macOS

Open Applications > Utilities > open Keychain Access
Locate your S/MIME certificate under My Certificates
Double-click > expand Trust section > set up:
- When using this certificate: Always Trust
- Secure S/MIME: Always Trust

2 - Enable experimental flags (if still not working)

Open Edge > access edge://flags/#enable-smime
Enable the following flags:
- #enable-smime
- #enable-experimental-web-platform-features

We look forward to hearing from you and reviewing the results. Please understand that our initial reply may not immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution. Thank you for your time.

Warm Regards,

Lychee-MSFT | Microsoft Q&A Support Specialist

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