Following the userbase suggestion on http://userbase.kde.org/Akonadi#Disabling_the_Akonadi_subsystem and changing StartServer=false I start kmail and it fails to start akonadi. Seems that the boolean not only disables start on login, it also disables autostart. Note that the error dialog kmail puts up is very unhelpful (the one with a list of very technical gibberish). Reproducible: Always
Sorry, the wikipage is wrong, I'll fix it. The option StartServer controls whether the database server should be started or not. You cannot disable starting Akonadi server on login. The server is not started on it's own, but it's always started because some other applications has requested it, usually it's the clock plasma applet. You can prevent the applet from starting Akonadi by unchecking "Display Events" in it's settings. However if you have any other applets that require Akonadi, or if KMail is automatically started after login, the Akonadi server will be started automatically anyway.
Fixing the docs is a fix too :) Thanks!