send email, recommended use 163 mailbox service, as it is tested.

    :param sender: str
        email address of sender
    :param pw: str
        password for sender
    :param to: str
        email addressee
    :param subject: str
        subject of email
    :param content: str
        content of email
    :param files: list
        path list of attachments
    :param service: str
        smtp server address, optional is ['163', 'qq']
    :return: None

def send_email(sender, pw, to, subject, content, files=None, service='163'):
    """send email, recommended use 163 mailbox service, as it is tested.

    :param sender: str
        email address of sender
    :param pw: str
        password for sender
    :param to: str
        email addressee
    :param subject: str
        subject of email
    :param content: str
        content of email
    :param files: list
        path list of attachments
    :param service: str
        smtp server address, optional is ['163', 'qq']
    :return: None
    """
    se = EmailSender(from_=sender, pw=pw, service=service)
    se.send_email(to=to, subject=subject, content=content, files=files)
    se.quit()