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 mail_list is empty then return False.
  
  assert validate_mail_list(["example.user@gmail.com", "bad@example"])==False
  assert validate_mail_list(["example.user@gmail.com", "another.user@yahoo.com"])==True
  assert validate_mail_list(["example@domain", "test@domain.com"])==False
  assert validate_mail_list(["valid.email@domain.com"])==True
  assert validate_mail_list([])==False
output: def validate_mail_list(mail_list):
      if not mail_list:
          return False
      for email in mail_list:
          if not ('@' in email and '.' in email and email.index('@') < email.rindex('.')):
              return False
      return True