After I have upgraded from Ubuntu 11.04 to 11.10 I discovered an issue on kmail – emails were not sent but stayed in the local “outbox” folder.
After some investigations I have found out, the reason was a disconnected “Mail dispatcher agent”. After I restarted the agent, the emails were sent immediately.
I found a useful application which made the restart quite easy – akonadiconsole. To install it simply run
sudo apt-get install akonadiconsole
After starting it, select tab “Agents”, select the “Mail dispatcher agent” and hit the restart button.