You can find the URLs for this dynamic content in System > Configuration > DOTMAILER > Dynamic Content > External Dynamic Content URL's.
Set up best sellers/most viewed
The products displayed within these dynamic content blocks makes use of the default Magento Bestsellers and Most viewed products reports, which can both be found in Reports > Products.
You also have the option to configure what time period we select these products over.
It's important that you've viewed the products and best sellers reports to ensure any products that could be returned over the selected time period remain enabled and in stock.
Select Save Config after making any changes.
Filter by category
In addition to pulling in content based on the selected time period, you are also able to filter these reports by adding a category ID to the end of the URLs we provide. This means, for example, you can ensure you only send the best sellers of your men's category to your male contacts.