I think this is a know iCloud problem.
If the correct (friendly) email address in not in the appointment/event there is no way to get it.
Could you post or send to us the raw eml data or appointment/event data as zipped attachment? You can find the support address on the bottom of this page.
The problem is with the organizer only.
The correct email is there, however it is only added as one of the key
parameters. This strange email is used as the true value of the ORGANIZER header:
I'm not sure what to think of this. It seems to me this format is incorrect. It looks like all replies should be sent to this 'strange' email, and the actual sender took great care to enforce that.
Mail.dll behaves correctly here.
You can extract the value of the "email" key parameter manually using this code:
string email = appointment.Event.GetHeader("organizer").GetKeyParameter("email");