Can you share what your scenario looks like and also what the collection of the array that you are iterating looks like?
What you can do is utilize,
{{distinct(2.array; “email”)}}
Whereby,
2.array is the array you are getting
email is the name of a property in your array, if it is nested you can use dot notation to access lower depth eg. contacts.email
This will be the input of your iterator, i.e if you are getting an array from the records then you can use this. But, I need to check what your collection looks like cause this might not work if a single collection holds multiple email addresses.