This method is preferred when you want your external users or clients also uses an email to initiate an App. However, the App may have many custom fields or there may be various conditions based on which you want to decide the initial state of the item. This is typically done with form on your web site that users fill and submitFor example, say you have a New Quote app where users can fill in what they want and you will provide a quote. This cannot be achieved by sending a "free form" email to specific address as in Indirect Interface. This will be better achieved by have a web form where users can pick which product they want, any specific parts or configuration and then submit their request. The form processing script will send can now generate an email with all the data including custom fields and send the email to the relevant address.
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