Cannot sign message in Outlook Web Access S/MIME when the sender's signing digital certificate is missing from the local system

Problem description

This problem is similar to the problem discussed in Cannot decrypt message in Outlook Web Access with the S/MIME control when the recipient's digital certificate is missing from the local system. In this case, the problem affects the ability to send digitally signed messages rather than receiving encrypted messages. Sending a digitally signed e-mail message first requires an e-mail client that supports S/MIME. Next, the e-mail client must be able to access the private key for the sender's signing certificate on the local machine or smart card to successfully sign the message.

When a sender attempts to send a digitally signed e-mail message in Outlook Web Access on a computer that does not have the private key for the sender's encryption certificate on the local computer or smart card, Outlook Web Access displays the following error message:

A digital ID that allows you to sign this message is missing.

Resolution

To resolve this issue, make the private key for the sender's signing certificate available on the Outlook Web Access computer. To make the certificate available, use any of the methods listed in Cannot decrypt message in Outlook Web Access with the S/MIME control when the recipient's digital certificate is missing from the local system.