If you set your order confimration subject to include an exclamation mark your email to your customer may be treated as spam.

You can edit the subject of your order confirmation by doing the following:

• Log into Joomla
• Select Components->Seber Cart Configuration
• Select Languages
• Select Email: Order Notification from the drop down and click on Select
• Edit item number 1 in the language editor.  This is the emails subject line
• Click on Save