S/MIME in Outlook for iOS / Android with Exchange on-premise?

Copper Contributor

Hello, I'm trying to figure out if the S/MIME-certificate-functionality in the Outlook app only applies to Office 365 or to Exchange on-premise as well (no hybrid). I don't see the option to enable S/MIME in the app for my Exchange account:

Exchange accountExchange account
















Here's a screenshot from the documentation with the security options:

Office 365 accountOffice 365 account


2 Replies

@adm8888I am having the same issue. Only when you select a Exchange Online account you get additional security options to add a digital certificate but not when you are using on-premise Exchange.


Apparently this hasn't changed since 2020.


I am completely baffled by this. Will have to go back to Android E-mail app which has the option to add a digital certificate for every mailbox.

Please Microsoft, add this functionality for on-premise mailboxes as well.



Also see;

New Contributor
‎Dec 10 2019 11:21 AM

@Ross Smith IV : Will Outlook for iOS ever support S/MIME for on-premises Exchange 2019? This is the only thing that prevents us from using the application. It is artificially hobbled in S/MIME support to just 365 accounts. iOS Mail, while in many ways inferior to what Microsoft has created with Outlook for iOS, at least supports S/MIME for on-prem.
Ross Smith IV
‎Dec 10 2019 12:51 PM

@SiobhanTX It's possible we'll be able to support S/MIME for on-premises accounts leveraging hybrid modern authentication (http://aka.ms/hmaom) once those accounts are migrated to the native Microsoft sync technology. We require an Exchange Online tenant because we're leveraging the S/MIME virtual cert collection for certificate validation (see http://aka.ms/omsmime for more information).