Whether problem or not, but I know: some e-mail filters throw away or into spam e-mails comming from php-mailer (function mail used in QC). The emails comming from smtp-server are treated better. So I've just programmed a method to send the order-email via smtp. Example properties of email (without and with smtp):
Received: from web4.pearl-online.net (web4.pearl-online.net [62.159.194.134]) by mail1.pearl-online.net (Postfix) with ESMTP id 7EFCD2D443 for <zakupy@kimla.de>; Sat, 21 May 2011 10:27:41 +0200 (CEST)
Received: from smtp.kimla.de (web4.pearl-online.net [62.159.194.134]) by mail1.pearl-online.net (Postfix) with ESMTPA id 09795201AB; Wed, 1 Jun 2011 08:46:13 +0200 (CEST)
Additional benefit: if the customer e-mail address doesn't exist (example a letter mistake) you will get the message from your e-mail provider (undelivered message). A standard mail sends emails like 'bottle in the sea'.
