uptime-kuma/server/notification-providers/smtp.js

const nodemailer = require("nodemailer");
const NotificationProvider = require("./notification-provider");
const { DOWN, UP } = require("../../src/util");

class SMTP extends NotificationProvider {

    name = "smtp";

    async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {

        const config = {
            host: notification.smtpHost,
            port: notification.smtpPort,
            secure: notification.smtpSecure,
        };

        // Should fix the issue in https://github.com/louislam/uptime-kuma/issues/26#issuecomment-896373904
        if (notification.smtpUsername || notification.smtpPassword) {
            config.auth = {
                user: notification.smtpUsername,
                pass: notification.smtpPassword,
            };
        }
        // Lets start with default subject and empty string for custom one
        let subject = msg;
        let customSubject = "";

        // Our subject cannot end with whitespace it's often raise spam score
        // Once I got "Cannot read property 'trim' of undefined", better be safe than sorry
        if (notification.customSubject) {
            customSubject = notification.customSubject.trim()
        }

        // If custom subject is not empty, change subject for notification
        if (customSubject !== "") {

            // Replace "MACROS" with coresponding variable
            let replaceName = new RegExp("{{NAME}}", "g");
            let replaceHostname = new RegExp("{{HOSTNAME}}", "g");
            let replaceStatus = new RegExp("{{STATUS}}", "g");

            // Lets start with dummy values to simplify code
            let monitorName = "Test"
            let monitorHostname = "example.com"
            let serviceStatus = "⚠️ Test";

            if (monitorJSON !== null) {
                monitorName = monitorJSON["name"];
                monitorHostname = monitorJSON["hostname"];
            }

            if (heartbeatJSON !== null) {
                serviceStatus = heartbeatJSON["status"] == DOWN ? "🔴 Down" : "✅ Up";
            }
            
            // Break replace to one by line for better readability
            customSubject = customSubject.replace(replaceStatus, serviceStatus);
            customSubject = customSubject.replace(replaceName, monitorName);
            customSubject = customSubject.replace(replaceHostname, monitorHostname);

            subject = customSubject
        }

        let transporter = nodemailer.createTransport(config);

        let bodyTextContent = msg;
        if (heartbeatJSON) {
            bodyTextContent = `${msg}\nTime (UTC): ${heartbeatJSON["time"]}`;
        }

        // send mail with defined transport object
        await transporter.sendMail({
            from: notification.smtpFrom,
            cc: notification.smtpCC,
            bcc: notification.smtpBCC,
            to: notification.smtpTo,
            subject: subject,
            text: bodyTextContent,
            tls: {
                rejectUnauthorized: notification.smtpIgnoreTLSError || false,
            },
        });

        return "Sent Successfully.";
    }
}

module.exports = SMTP;