Version: 1.10.0 (using 4.1.1 (KDE 4.1.0 (4.1 >= 20080722)) "release 40.1", KDE:KDE4:Factory:Desktop / openSUSE_11.0) Compiler: gcc OS: Linux (i686) release 2.6.25.11-0.1-pae I can't say exactly the number of letters, but if the folder contains near 5000 of letters, it works, but if it contains more than 7000 (7400 in my case), it cause kmail to operate extremely slow.
*** This bug has been marked as a duplicate of bug 163469 ***