i might have a similar problem: mail connection loading forever, mail client not resonding, not being able to open it again without rebooting, .just works occasionally.
i also tried that fix again that you refer to but neither with nor without root access it actually DOES anything (just jumps in the next input row). does it execute the command in your case?
ls -la /home/user/ | grep qmf
mv /home/user/.qmf/ /home/user/.qmf.bad/
rm -rf /home/user/.qmf.bad/