I uninstalled Kontact and Kmail from my Debian install. I later re-installed and since then Kmail opens in a separate window rather than within Kontact as it did before I uninstalled.

The 'Mail' icon is present in Kontact and when clicked on just brings the already open Kmail window to the front.

I've looked through the various settings and can't find anything obvious, so if anyone has a solution to this admittedly small annoyance it would be appreciated.