If you have an invitation in your KMail inbox you can either press Reject to ignore the request, or press Accept or Accept Cond.. The last two actions will insert the item into your calendar. In any case, KMail will send your response to the organizer automatically.

You can also Delegate or Forward the invitation. When delegating, you can suggest another person as your proxy. Using Forward you can forward the invitation to one or more people not yet invited. When the receiver of the delegation or forward accepts the invitation, the organizer will be asked to approve the new attendee.

If for any reason you changed your mind, edit your status in the item's attendee tab. If you checked the Use Groupware Communication box in the KOrganizer group scheduling configuration, KOrganizer will ask you to send an email updating your attendee status. If not, choose the Schedule → Send Status Update menu item to send your status update.

If you are not satisfied with some of the characteristics of the event or to-do you got invited to, and want to send a counter proposal to the organizer (for instance an alternative location or time), just edit the item and send it back as your proposal, by selecting the item and choosing the Schedule → Request Change menu item.

The organizer of the event will get your proposal by email, and will be able to accept it or decline.

To request the latest version of an event or to-do, select the item, and choose the Schedule → Request Update menu item. The organizer should then send you back the latest version of the item.