It would be nice to have ability to append some headers to email notifications. I meant 4th parameter to mail() function ( http://www.php.net/manual/en/function.mail.php ).
In my opinion, it should be customizable either from AdminCP or from config.php
For example, when I've got non-latin symbols in task/user names or localized strings I have to add encoding information into email header. Something like "\r\nContent-Type: text/plain; charset=utf-8".
Now this task cannot be done without patching the source.
I think the default encoding for sending emails should be utf-8.
I agree that email encoding should be utf-8 (and now it's definitely so), but some email clients can not determine it without header which explicitly "tells" them about this fact.
I added the UTF-8 content type to most if not all mail() calls.
Maybe just add fixed encoding string to mail headers without any configuration?