Table schema:
CREATE TABLE party_forms (form_id VARCHAR); CREATE TABLE parties (party_email VARCHAR, party_id VARCHAR); CREATE TABLE party_forms (party_id VARCHAR, form_id VARCHAR)

Question: Find the emails of parties with the most popular party form.
SQL: SELECT t1.party_email FROM parties AS t1 JOIN party_forms AS t2 ON t1.party_id = t2.party_id WHERE t2.form_id = (SELECT form_id FROM party_forms GROUP BY form_id ORDER BY COUNT(*) DESC LIMIT 1)