To send email
        :param to: the recipients, list or string
        :param subject: the subject
        :param body: the body
        :param reply_to: reply_to
        :param template: template, will use the templates instead
        :param kwargs: context args
        :return: bool - True if everything is ok

def send(self, to, subject=None, body=None, reply_to=None, template=None, **kwargs):
        """
        To send email
        :param to: the recipients, list or string
        :param subject: the subject
        :param body: the body
        :param reply_to: reply_to
        :param template: template, will use the templates instead
        :param kwargs: context args
        :return: bool - True if everything is ok
        """
        sender = self.config.get("MAIL_SENDER")
        recipients = [to] if not isinstance(to, list) else to
        kwargs.update({
            "subject": subject,
            "body": body,
            "reply_to": reply_to
        })

        if not self.validated:
            abort("MailmanConfigurationError")

        if self.provider == "SES":
            kwargs["to"] = recipients
            if template:
                self.mail.send_template(template=template, **kwargs)
            else:
               self.mail.send(**kwargs)

        elif self.provider == "SMTP":
            if template:
                data = self._template(template=template, **kwargs)
                kwargs["subject"] = data["subject"]
                kwargs["body"] = data["body"]
            kwargs["recipients"] = recipients
            kwargs["sender"] = sender

            # Remove invalid Messages keys
            _safe_keys = ["recipients", "subject", "body", "html", "alts",
                          "cc", "bcc", "attachments", "reply_to", "sender",
                           "date", "charset", "extra_headers", "mail_options",
                           "rcpt_options"]
            for k in kwargs.copy():
                if k not in _safe_keys:
                    del kwargs[k]

            message = flask_mail.Message(**kwargs)
            self.mail.send(message)

        else:
            abort("MailmanUnknownProviderError")