emails = "[email protected], [email protected], [email protected], [email protected]"

User.rb (id,email)

User.where("email IN (?)", emails)
  User Load (1.0ms)  SELECT "users".* FROM "users" WHERE (users.deleted_at IS NULL) AND (email IN ('[email protected],, [email protected], [email protected], [email protected]'))
 => []

emails = "[email protected], [email protected], [email protected], [email protected]".split(', ')

User.where(:email => emails)