How to send digitally sign S/MIME messages with Powershell cmdlet Send-MailMessage?

Question

Hello,
using AD Windows PKI I assigned a certificate EKU (1.3.6.1.5.5.7.3.4) to sign emails and get this with
autoenrollment also to my CERT Store PS
CERT:\CurrentUser\UserDS\ or the certificate could found via MMC / certificates in the store structur under "Active Directory User Object".
Signed messages (red icon) to send as S/MIME message using Outlook 2010 is not a problem.
Using PowerShell cmdlet Send-MailMessage to be sent company notification for a new passwordpolicy some days before pwd expired?! I use the cmdlet already successfully to filling HTML bodies with variables and send to individuals accounts.
Reduced simplified PS code:
$SMTPBodyHtmlTemplate = Get-Content "C:\PS\Template\HTMLBody.html" | Out-String
Function SendEmailNotification # /* SEND E-MAIL Notification to User */#
[string] $SMTPServer = "mail.domain.local"
$CurrentUser = "$env:username"
[string]$SMTPFrom = (Get-ADUser $CurrentUser -properties mail).mail
[string[]] $SMTPTo = $($Obj.EmailAddress)
[string]$SMTPSubject = "Notification!"
[String]$SMTPBodyHtml = $SMTPBodyHtmlTemplate.Replace("UserDisplayname","$($UserDisplayname)")
Send-MailMessage -From $SMTPFrom -To $SMTPTo -Subject $SMTPSubject -BodyAsHtml $SMTPBodyHtml -dno OnFailure -SmtpServer $SMTPServer -encoding ([System.Text.Encoding]::UTF8) -ErrorAction Continue
How can I use the PSDrive own CERT and using PowerShell cmdlet Send-MailMessage
to send a signed message, without development experience?
Thanks in advance for cooperation.
Manfred Schüler

Answer 1

Hi,
could create with an other colleague a DLL file (with this informations) for successfully sending sign messages from PS-Script. 
Function SendEmailNotification # /* SEND SIGN E-MAIL */#
$SMTPBodyHtmlTemplate = Get-Content "C:\PS\Template\HTML.html" | Out-String
[System.Reflection.Assembly]::LoadFile("C:\PS\Assembly\Cpi.Net.SecureMail.dll") | Out-Null
[string]$strSmtpServer = "smtp.domain.local"
[string]$strSmtpPort = "25"
[string]$strFrom = (Get-ADUser $CurrentUser -properties mail).mail
[string]$strFromAlias = (Get-ADUser $CurrentUser -properties DisplayName).DisplayName
[string]$strTo = $UserEmailAddress
[string]$strToAlias = $UserEmailDisplayName
[String]$strSubject = "Subject as you like"
[string]$strBody = $SMTPBodyHtmlTemplate.Replace("UserDisplayname","$($UserDisplayname)")
$objMail = New-Object Cpi.Net.SecureMail.SecureMailMessage
$objFrom = New-Object Cpi.Net.SecureMail.SecureMailAddress($strFrom,$strFromAlias,$objCert,$objCert)
$objTo = New-Object Cpi.Net.SecureMail.SecureMailAddress($strTo,$strToAlias)
$objMail.From = $objFrom
$objMail.to.Add($objTo)
$objMail.Subject = $strSubject
$objMail.Body = $strBody
$objMail.IsBodyHtml = $TRUE
$objMail.IsSigned = $TRUE
$objMail.IsEncrypted = $FALSE
$objSMTPClient = New-Object System.Net.Mail.SmtpClient($strSmtpServer,$strSmtpPort)
$objSMTPClient.Credentials = [System.Net.CredentialCache]::DefaultNetworkCredentials
$objSMTPClient.send($objMail)
Maybe Microsoft can implement this in future versions of the cmdlets Send-MailMessage ;-)
Manfred Schüler