After being able to add a shared mailbox on Outlook mobile (see https://t.co/MkG56cl1TT), another long awaited feature is now available on your Outlook mobile application: the use of SMIME.
To start using, you need of course an SMIME certificate – I will not go in details there on how or where to get SMIME certificates, reach out either to your IT support or on the Internet 
.
NOTE support for S/MIME certificate issuing and delivery using application configuration for enrolled devices will come in the future.
Then reach out to your mobile and open the Outlook mobile app to go to the Settings and access the email account you want to enable for SMIME – if you have multiple accounts, you will have to do it for each of them
Then click on Security
And turn on S/MIME; the application will have to restart after turning S/MIME on
NOTE turning on S/MIME will disable the thread view (aka Organize by thread) if you have it enabled
Then next time you write an email and want to sign and/or encrypt it with S/MIME just use the “more” menu (Android device) to choose the S/MIME option
Off course, if you don’t have an S/MIME certificate installed, you will not be able to do anything other than just viewing S/MIME message (being shown as ‘attachment like)
As soon as I read your blog post, I updated Outlook for my Android Galaxy A40, and turned on S/MIME.
While I actually have a properly installed S/MIME certificate and priv key installed for VPN and apps, matching the configured email address on Outlook for Android, regretfully Outlook keeps stating : We couldn’t find your S/MIME certificate. Install a certificate or please contact your IT help desk.
I’m actually the IT Help Desk and I have no clue why this error is occurring.
I’m sorry but can’t tell
You have to take a look at the Outlook mobile app logs (Settings\Help & feedback\Collect diagnostics)