From kde mailing lists:

Hello everyone!

If you use KMail (or Kontact), please help us, the KDE PIM developers, to get
a better picture of how you use it so that we know which parts of the
software we should focus on, and how we should evolve it in the future. We
will use the results of the survey to make the experience of using KMail as
best as possible for everyone.

You can fill the survey here: It
won't take you more than 5 minutes.

Also please remember to spread the word about the survey to other KMail users
so that we get as many responses as possible.

Thank you very much!