This can be changed in the browser file handling option. To change this option go to:
1. Central Admin\Application Management\Manage Web Applications.
2. Select General Settings for the specified web application
3. For Browser file handling, select permissive. The default is strict.
If we need to keep this option for security.
SharePoint 2010 put these types static in code, You need to create HTTPModule to remove attachment from its header. Example in code below: