Send encrypted email with PR_SECURITY_FLAGS

Question

I want to send an encrypted email.

I found this PR_SECURITY_FLAG code here on StackOverflow.

Const PR_SECURITY_FLAGS = "schemas.microsoft.com/mapi/proptag/0x6E010003"

FilePath = Application.ActiveWorkbook.FullName
FileName = Application.ActiveWorkbook.Name

Dim OutApp As Object
Dim OutMail As Object

Set OutApp = CreateObject("Outlook.Application")
OutApp.Session.Logon
Set OutMail = OutApp.CreateItem(0)

ulFlags = ulFlags Or &H1 ' SECFLAG_ENCRYPTED
ulFlags = ulFlags Or &H2 ' SECFLAG_SIGNED

With OutMail
    .to = recipient
    .Subject = FileName
    .HTMLBody = body & "<br>" & .HTMLBody
    .PropertyAccessor.SetProperty PR_SECURITY_FLAGS, (ulFlags)
End With

I get

Run-time error '5': invalid procedure call or argument

on the .ProperyAccessor line.

I tried putting it in and out of the With statement.