If you'd like to ask for email in your ethnio screener, and then pass that to an external tool like Surveymonkey.com that supports external variables, you can easily do that under screeners >> logic. The idea behind this is that you'd like to not ask people for their email twice, so it's a pretty elegant way of handing people off to another tool, and just using ethnio as the gateway to decide who gets invited to whatever tool you're using for research.
The most important step is to tell whatever tool you're using that the name of the variable is "email." We use the fairly standard syntax that will look like this when your participants clicks through:
So keep in mind you will be passing emails as plain text along with the URL, which could violate some privacy policies. If that's the case, don't use this feature. :-)