S/MIME encrypted messages cannot be sent with Outlook for iOS: "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.

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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

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

Possible causes

Related links:

External sources