In my opinion, Akonadi, Nepomuk, and Strigi are the worst features foisted upon KDE4 users. The KDE4 developers must have thought bugs fixes were boring and figured, 'let's do something cool, with really weird names' so that's what we got. To put it bluntly, those programs are Windows like in that they are intertwined within KDE4 and you can't uninstall 2 of the 3. Kmail and Kalarm were two of the best KDE apps that were totally ruined by those programs.
At least we can disable Akonadi and Nepomuk, and uninstall Strigi, if you're not a big PIM guy, without consequences.
To disable Akonadi edit .config/akonadi/akonadiserverrc and change...
... log out and in again.
Your computer will thanks you and you can still use web based email without problems. BTW, Claws-mail is very similar to kmail and is blazing fast if you need an ISP based email client.