I’m making an Add-in for Outlook using VSTO 2005 SE and C#.

I have made some code that attaches UserProperties to mails and archives
them in an external application as .msg files.

Later, if the .msg mails are opened in Outlook, I need to be able to compose
a reply with the same UserProperties as the original mail.

If I just press the reply button, all UserProperties are lost, and I can’t
seem to find my way back to the original mail.

All functionality requires human interaction: A human decides what
UserProperties to add, when a reply is needed, and writes the reply.

What are my options?

Regards,
Philip