Sending S/MIME encrypted messages with Outlook for iOS is not possible: "There's a problem with one of your S/MIME encryption certificates."

Assume the following scenario:

• The certificates were transferred to the smartphone via the Intune Connector.
• Reading encrypted messages works.
• However, when enabling encryption for outgoing messages, the following error message is displayed:

There's a problem with one of your S/MIME encryption certificates. Contact your IT help desk for more info.

There is a problem with one of your S/MIME encryption certificates. Contact your IT help desk for more information.

Possible causes

• The certificate chain was not uploaded to the Virtual Certificate Collection in Exchange Online.
• The certificate revocation list has not been published to the Internet. The revocation lists associated with the S/MIME certificates must be accessible from the Internet.

If Exchange Online fails to locate a trusted root certificate or fails to contact the certificate revocation list for the certificate authority, that certificate is considered invalid and is not trusted.

S/MIME for Outlook for iOS and Android in Exchange Online

Related links:

• Transferring S/MIME certificates to Microsoft Intune

External sources

• S/MIME for Outlook for iOS and Android in Exchange Online (Microsoft Corporation)
• Configure S/MIME in Exchange Online (Microsoft Corporation)
• How to Configure S/MIME in Office 365 (Microsoft Tech Community)
• S/MIME Certificate not trusted in Office 365 (OWA and Outlook iOS app) (Microsoft TechNet Forums)
• Outlook for iPhone IOS 14 S/MIME Certificate untrusted (Microsoft TechNet Forums)