With Outlook Web Access

Sometimes, when reading an OWA signed e-mail, a message is displayed indicating the certification authority is not allowed/recognized. Probably because the intermediate or root certificate has not been installed in the local computer of the OWA server.

Microsoft documented the issue here:

• http://technet.microsoft.com/fr-fr/library/bb123793.aspx
• http://technet.microsoft.com/fr-fr/library/aa998056.aspx

Microsoft advises to import the missing certificate(s) on the Exchange server.

• http://technet.microsoft.com/fr-fr/library/aa995734.aspx
• http://technet.microsoft.com/fr-fr/library/aa998899.aspx

See our documentation as well: Install intermediate or root certificates manually

Concerning TBS client certificates, the certificates to import are available on TBS X509 CA persona

OWA can be used to sign and encypher emails. However your certificate must have been published in the Active Directory in order for Exchange to access it and realize the operations.

Here is Microsoft documentation: http://technet.microsoft.com/fr-fr/library/aa997794.aspx