I've run Desknow for 3 years - as a standalone POP/SMTP/Webmail solution and as a Webmail portal on top of an existing POP/SMTP server and I can say with great amazement that the program has never ever crashed (though there are only 8 email accounts on my server - hardly high load). The only real concern with Desknow is that it takes a big tax on RAM due to its dynamic HTML generator engine.

I can't say that it WON'T crash, but I can say that it DIDN'T.