Also, in order to build the function, the service needs to collect data about both spam and non-spam emails. So simply providing a function that allows you to

Also, in order to build the function, the service needs to collect data about both spam and non-spam emails. So simply providing a function that allows you to calculate a score isn't enough; they would need (at least a large percentage of) users to send back information about their email contents as well. (Like embedded links, as mentioned in the post.)