Limiting the email recommendations widget to specific categories, brands or other product attribute can be done by selecting the "Recommended items based on product attributes" widget type.

You can then select an attribute and the values you would like it to contain, or not contain. You can add multiple values and attributes as show in this video tutorial

If the user visited the site and viewed products that match the selected attributes , personalized recommendations will be presented , otherwise the user will see the top sellers. You can force top sellers by changing the dropdown box     

*Note that product attributes need to be setup by Barilliance before you can use this functionality. Attributes will be taken from your product data feed.