Powershell S/MIME - email

Question

Currently, each day my business needs to send and encrypted email using MS Outlook. The process works, but obviously the whole 'doing it every day thing' sucks. I've tried looking up ways to automate the process which has helped me solve the surrounding processes, but i still can't find anything, or whip up anything myself which will handle the email side. The flow of events are;
Receive
Encrypted email is received
Email is opened and attachment is dragged to UNC share 1 (repeated for each email recieved)
Attachment is picked up and processed by surrounding script
Send
Browse UNC share 2
Copy 1 of x files to a new email
Set subject as full file name
Select email to be signed/encrypted in top ribbon
Send email and repeat for each file in UNC share 2
I can get emails to send with attachment via powerhsell and by using S/MIME, but once I combine the two I get stuck and the script turns to rubble :(
Any help at all would be greatly appreciated

Answer 1

If I'm not mistaken, Powershell can load and use .NET assemblies, correct? (I'm not a powershell user, so my knowledge is limited).
Given that, I would recommend taking a look at using the MimeKit and MailKit libraries.
Check out the MimeKit README for some examples on how to use the S/MIME API's.
MimeKit comes with a WindowsSecureMimeContext which you might be able to use out of the box, but that depends on where your private keys and certificates are stored. If they aren't in the X509Store, then you could use the TemporarySecureMimeContext and simply load the certificate(s) and private key(s) into that and use it.

Answer 2

Got a similar problem and here's my solution so far, still testing:
$Outlook = New-object -ComObject Outlook.Application
$Mail = $Outlook.CreateItem(0)
$Mail.To = "me#company.tld"
$Mail.Subject ="Test"
$Mail.Body ="Test Body"
# 0 = nothing, 1 = encrypt, 2 = sign, 3 = both!
$PR_SECURITY_FLAGS = "http://schemas.microsoft.com/mapi/proptag/0x6E010003"
$Mail.PropertyAccessor.SetProperty($PR_SECURITY_FLAGS, 3)
$Mail.Send()
If Outlook is running, everything works fine. But when I start Outlook afterwards, I will find the created Mail in the Outbox without encryption and not signed.
Without Outlook running, the Code would produce an "InvokeMethodOnNull"-Error. Putting a $Mail.Display() before the SetProperty()-Part would take care of that and the buttons seem to be checked in the opening E-Mail, but the result will be the same: Start Outlook and your mail is in Outbox without encryption and not signed.