Along the lines of my earlier post about e-mailing.
Have you ever been part of an e-mail chain where the subject morphed from the original to something else?
Don't be afraid to change the subject line or recipients of an e-mail chain or delete non-relevant sections. In addition to intellectual property issues, there can be a lot of waste associated with not keeping the e-mail header information current.
E-mail is pervasive and many people get hundreds of e-mails a day. If your subject does not communicate effectively, your message won't even see the light of day.