When editing a message as new, relevant/appropriate headers should be kept, e.g. "In-Reply-To" and "References".
- you reply to a mail on a mailinglist, but it gets sent only to the original author (because of using "Reply" and not "Reply All")
- you want to resend it to the mailinglist
- you go to "Sent", "Edit Message As New", and resend it
- the threading is broken
I think SquirrelMail should use the original headers (as default) and overwrite the ones it uses currently.