Users often send documents to each other as Outlook attachments.  Depending on how the attachments are opened from Outlook, they may even be editable, so the attachment can be edited and then forwarded to another recipient.  However, users with InfoPath 2007 Sp1 will find that InfoPath forms attached to emails will always open read-only.  New functionality in Outlook 2007 and InfoPath 2007 makes the old attachment functionality obsolete.  This article discusses the changes and how the new functionality can be used to benefit workflow situations.

Editing InfoPath forms attached to Outlook emails