Bug 26603: Missing dependency on kdepim-kio-plugins was closed after adding kdepim-kio-plugins to kmail's recommendations (as I understand it). It is my and other users' belief[1] that recommends is not enough as it provides "a significant amount of functionality" that is no less central than the built-in POP3 support, and that kmail should depend rather than recommend the plugins package.
When attempting to use an IMAP account (configuration options being fully available even without the plugins installed), the error message produced on the command line is: kmail: ERROR: : couldn't create slave : Unable to create io-slave: klauncher said: Unknown protocol 'newimap'. The GUI message box error is even less informative, and is unfortunately what most end-users will see. Given the nature of the error message, the integral role of IMAP functionality in an e-mail program, and the presence of GUI elements for it, we hope that you will consider this matter once more. I would be happy to provide any further information requested to assist in the matter. Thank you. [1] http://lists.debian.org/debian-kde/2004/08/msg00274.html -- Alex Nordstrom