If an email is set regarding in Outlook is that field present on the Create message?

I am looking to write a Plugin or Workflow Activity which will fire when a user has forwarded / sent and email and set regarding to an account for example.

I wondered at what point the regarding field would be set in the process.  Does it come in on the Create message or is it processed in the Update message just after the creation of the email.

Would be ideal and simpler if I am getting it in the Create message as it might get difficult to tell the difference between the Outlook based set regarding and a subsequent set regarding done through the CRM interface.