Outlook - POwerShell - Getting message headers

# Get Internet headers from MailItem in PowerShell
Add-type -assembly "Microsoft.Office.Interop.Outlook" | out-null
$OutlookApp = new-object -comobject outlook.application
$MAPI = $OutlookApp.GetNamespace("MAPI")
$Message = $MAPI.GetDefaultFolder([Microsoft.Office.Interop.Outlook.OlDefaultFolders]::olFolderInbox).Items.GetLast()
$Message.PropertyAccessor.GetProperty("http://schemas.microsoft.com/mapi/proptag/0x007D001E")
$OutlookApp.Quit()

More information here

https://msdn.microsoft.com/en-us/library/bb176395%28v=office.12%29.aspx