Wish I could have helped more.
One of the things I have learned when working with almost anything in Linux is that completely removing it and starting over with defaults settings and changing 1 thing at a time and working on 1 problem at a time often ends up being faster than trying to do it all at once.
As for alternatives, I have heard good things about RoundCube.
Depending on your situation it may nopt be appropriate so be sure to do some research first.
If you decide on a web-based solution, be aware that MOST people have difficulty with a Horde/IMP setup. It looks promising, but its pretty complex as I understand it.
Good luck with everything,