class Contact:
    all_contacts = []
    
    def __init__(self, name, email):
        self.name = name
        self.email = email
        Contact.all_contacts.append(self)
        
class MilSender:
    def send_mail(self, message):
        print("Sending mail to " + self.email)
        
class EmailableContact(Contact, MilSender):
    pass

e = EmailableContact("John Smith", "j@qq.com")

Contact.all_contacts

e.send_mail("Hello, test e-mail here.")