to use waterfall approach you can click on a new column and choose waterfall
then choose what kind of data you want. which it is email in your case
after that click on add action and go ahead choose the providers you want to use.
you can select multiple providers there
a suggestion - use lower cost provider on top so if you already found a match at low cost you dont need to go for the provider with higher cost
in waterfall query will run in sequence so just choose the provider you are comfortable with on top of the waterfall