input: Write a function to validate an a list of emails. The function should return a boolean indicating whether a given email address is valid. If the given list is empty then return True.
  assert validate_mail_list(['example.user@gmail.com', 'bad@example'])==False
  assert validate_mail_list(['user123@gmail.com', 'another.user@domain.com'])==True
  assert validate_mail_list(['valid@email', 'another@valid.co.uk'])==False
  assert validate_mail_list([])==True
output: def validate_mail_list(emails):
      if not emails:
          return True
      for email in emails:
          if '@' not in email or '.' not in email.split('@')[1]:
              return False
      return True