I migrated to Ubuntu a good while ago (8.04?) and found Kmail to be much
more to my liking than Evolution. Simply installing kmail (and dependencies)
with Synaptic worked fine. Eventually I upgraded to 10.04 and have had problems - I installed kmail and it seemd to work OK initially, but I
got various problems with address book and kept getting popups saying
'invalid response from server' messages. I have now installed Kontact and
that seems to have got rid of the invalid response messages, but I'm still
having problems with my address book. I set up a distribution list in
addressbook, but it didn't appear in kmail. Workaround: type in the
addresses on a composer window and save the list - that works OK, but
it seems the wrong thing to do.

I keep getting error messages from Akonadi saying 'unknown error with no transaction'. Checking the Akonadi status it reports Nepomuk isn't running.
I can't find a package called nepomuk to install, so how do I fix that?

Sorry this is a bit rambling. I'll be happy to provide more details if someone can offer guidance.

Nepomuk should already be installed as part of your system. Please head to System Settings > Desktop Search and make sure Nepomuk (not Strigi!) is ticked.