Comment 22 for bug 482496

(In reply to comment #21)
> This patch will lead to a lot of mails that are unreadable on
> the other end. Not because the mail is incorrect, but because the recipient's
> software does not understand UTF-8.

This patch only changes the last resort.

> Can we maybe have a configurable list of encodings (try iso-8859-15 first,
> then iso-2022-jp, then default to utf-8)? any possible other ways to solve
> this?

You already can, that's what the intl.fallbackCharsetList.* pref "family" is for. You can configure global encoding defaults in Mail&News -> Character Encoding, but we don't have a pref panel for configuring custom fallbacks.
In either case, please file new bugs for any problems/regressions with this one.