Is it possible to sign subscribers up as follows:
* Step 1: add their email to the list
* Step 2: on the "thank you" page, ask them for their Interests
* Optional step 3: if they fill out the form, update their details with interests
if they don't want to fill out the form, they can just navigate back to the previous page. But this way you could capture the emails from the simplest possible one-field form, but if people had the time, capture more detail after that.
So sorry it's been so long in our reply - this question slipped under our radar! We don't have any built in tools that would allow for a two-part subscription, however, if you have development talent on board, you could likely accomplish this by building your own two part subscription form using our api. Hope that helps, John!