Version:            (using KDE KDE 3.3.1)
Installed from:    Gentoo Packages

I don't think that everybody will agree to this but I thought a while about it and I like the idea... :-)

Anyway, I found out that KMail has a usability-problem for power-users.
When using mutt, one simply has to press 'g' for 'group reply' to answer all daily mail. Mail-Followup-To is used (and so are mailing lists with other power-users that set this header field), simple mail is replyed normally, 'cc-parties' can be done with this. 
To achive these three cases in KMail, one has to press different buttons.
'reply to all' can not respect Mail-Followup-To because only the 'reply to list' function is there for this.
On the other hand, 'reply to list' cannot work with simple messages because if no list is detected, an empty recipient field is set.

So there is an pseudo-intelligent 'reply' feature, that chooses 'reply to list' if a list is found and 'reply to sender' if not.
This behaviour breaks 'cc-parties' because 'reply to sender' throws out all cc-field entries.
This could be fixed if 'reply' would not fall back to 'reply to sender' but to 'reply to all'. 

After thinking about this for a while, I could not find any disadvatages of that. 
There should be no change if one replies on single mail messages (if reply-to is handled correctly).

This improvement would make two things better in this world:
1. power users would only have to use *one single* reply function for (nearly) all mail messages
2. other KMail users would respect Cc entries set by the original poster. :)

Additionaly: mutt implements 'Mail-Followup-To'-handling in 'group reply' (which is 'reply to all') and does not provide an option to reply to *really all* mentioned addresses. The proposed solution for KMail would make it possible to do both. As long as I can see, KMail doesn't make a difference between 'reply to mailing list' and 'use Mail-Followup-to', but that's not a problem (for me).