SpamZilla connects to many different API's to get all the data into one place.  We wont lie, this isn't cheap, it costs a lot to maintain all this data.  This required us to use minimum metrics as a "cost effective foundation" when gathering all this data.

We start off by running all domains through Majestic to cast a wide net.  This data is used for our baseline.

As an example:

SpamZilla Score Generation: Auction Domains: Only domains with a minimum TF greater than 0 and more than 24 referring domains will be sent to SpamZilla to process for automated spam checking.  Expired Domains: Only domains with 8+ referring domains that are available will be sent to SpamZilla to process for spam checking.

As you can see in the image below, we haven't retrieved all the metrics for many domains and that's because they didn't meet the minimum requirements we've set when first getting their Majestic data.

The good news is you can select any domain you wish to send through SpamZilla for further processing.  This is using Custom Domain Lists and is described here.