I’m trying to extract the signed data object from mailItem created by Outlook in OnSent event to add an extra signed attribute. Is there any way to extract and update the signed data, but also to make sure that Outlook will not delete my custom signed attribute?

I’ve tried to take a look using Outlook Spy on the properties exposed and Redemption to convert the message into SecureMailMessage, but the problem is that there is no EntryId set. And, on top of that, how do I recreate the mailItem and make sure that the message format wasn’t somehow affected.