S/MIME configuration for Microsoft Outlook on the web OWA

Hello

I have a platform based on Windows servers,

I have an Exchange 2013 mail server with an OWA web access application.

I need to enable electronic signature of emails by accessing through OWA.

the certification authority that will be used is on another server under windows as well

I have set the S/MIME settings as follows:

Set-SmimeConfig -OWAAllowUserChoiceOfSigningCertificate $true
Set-SmimeConfig -OWAAlwaysSign $true
Set-SmimeConfig -OWACheckCRLOnSend $true
Set-SmimeConfig -OWAClearSign $true
Set-SmimeConfig -OWACRLConnectionTimeout 60000
Set-SmimeConfig -OWACRLRetrievalTimeout 10000
Set-SmimeConfig -OWADisableCRLCheck $true
Set-SmimeConfig -OWAForceSMIMEClientUpgrade $true
Set-SmimeConfig -OWAIncludeCertificateChainAndRootCertificate $true
Set-SmimeConfig -OWASenderCertificateAttributesToDisplay *********
Set-SmimeConfig –OWASigningAlgorithms 800C
Set-SmimeConfig -SMIMECertificateIssuingCA $([byte[]](Get-Content -Encoding byte -Path "C:\certs\issuer&root.sst" -ReadCount 0)

the file issuer&root.sst was imported from the CA

I have installed owasmime.msi for Internet explorer

but unfortunatly it doesn't give me the ability to sign

both fields: 
encrypt this message
and 
digitally sign this message
are in grey

in parameters I have set to choice automatically the certificate

How could I find solution for the problem? please

Thank you