public String toString() {
            StringBuilder email = new StringBuilder();
            if (from != null)
                headers.put("From", concatEmail(from));
            if (!to.isEmpty())
                headers.put("To", buildEmailList(to));
            if (!cc.isEmpty())
                headers.put("Cc", buildEmailList(cc));
            if (!headers.containsKey("Date")) {
                headers.put("Date", emailFormat.format(new Date()));
            }
            for (Map.Entry<String, String> entry : headers.entrySet()) {
                email.append(entry.getKey());
                email.append(": ");
                email.append(entry.getValue());
                email.append("\n");
            }
            email.append("\n");
            email.append(body);
            return email.toString();
        }