Automatic Email Manager is set by default with a common list of file type to process when they come as attachment. You can add new file extension or disable some extensions. It is easy with file types management, see how:
1. To access the file types management: Click on top menu 'File', then 'Options', section 'Email attachment' and click on 'File types Management'.
In the extension search enter the extension you want to edit, when found just click on button 'Process?' to say 'No'. That's all!