Fix bug. My (small) IMAP server crach when I connect several mail client in same time. I am trying to fix this bug

Nb: I dont accept offer > €50! I have a (very small) multi-threadin imap server written in C++ (Qt5 C++), and now when I connect several mail client to this server it crach. I think it is a threadin problem... so I need to correct the bug. It is necessary that the server accepts multiple connection with several client at the same time and for a long time. I think you need see about QRunnable, QThreadPool, QMutex and sure "Qt asynchronous" I sent you this (small) server, you compil it under Qt5 windows & linux and fix this crach. Code must be writin with Qt5C++ (not GNU C++). So we write "QString myVariable" and not "std::string myVariable". Server must running under 32 and 64 bit (windows & linux)