[otrs] Notification on new ticket

Hello all I successfully installed OTRS and its working nice and fast (mod- perl). I have just a small problem/question: If a customer sends in a mail and a new ticket gets created, he doesn't get a notification as expected. Is this an issue in 2.3.4 -version or do I have to config something? I found the text which should be sent, but the first mail isn't sent. Sending mail works fine (notification about closing, adding notes, etc. is received). Thanks for any help. Kind regards Roman