Mailing List Netiquette Enforcement Via Software?

Rob Kaper asks: "While administrating various e-mail mailing lists (with ezmlm), I noticed that most users lack an understanding of Netiquette. For example, they send their reply above the original, while quoting the entire original message. I could of course tighten the list policies and kick off offenders, but that would be a rather harsh solution. Is there software available that enforces or stimulates obedience of the Netiquette guidelines? (for example mailing list software that reformats ugly replies, converts HTML to plain text or bounces such e-mails)" Such programs would be useful to mailing-list maintainers who have bandwidth quotas. Any clues?