部署在A2托管的Node.js应用nodemailer/mailgun传输功能失效问题

部署在A2托管的Node.js应用使用nodemailer+mailgun处理邮件请求，本地运行完全正常，部署后无法正常发送邮件，不清楚如何查看服务端控制台输出验证运行状态。

const nodemailer = require('nodemailer');
const mailGun = require('nodemailer-mailgun-transport');
require('dotenv').config();

const key = process.env.MAILGUN_API_KEY;

const auth = {
    auth: {
        api_key: `${key}`,
        domain: 'MY DOMAIN'

    }
};

const transporter = nodemailer.createTransport(mailGun(auth));

const sendMail = (email, firstName, lastName, phone, helpType, message, cb) => {
    const pcsEmail = {
        from: email,
        to: 'MY EMAIL',
        subject: 'A new message from your website',
        text: "Name: " + firstName + " " + lastName + "\n" + "Phone Number: " + phone + "\n" + "Type of Help: " + helpType + "\n" + "Message: " + message
    };

    const confirmEmail = {
        from: 'MY EMAIL',
        to: email,
        subject: 'Email confirmation',
        text: "Hello there " + firstName + "," + "\n" + "\n" + "Thank you for contacting Pisgah Climbing School. The following email was sent to Pisgah Climbing School:" + "\n" + "\n" + message + "\n" + "\n" + "A PCS representative will contact you soon!"
        };

        Promise.all([
            transporter.sendMail(pcsEmail),
            transporter.sendMail(confirmEmail),
        ])
            .then((res) => console.log(res))
            .catch((err) => console.log(err));

}; 

exports.sendMail = sendMail;

• 环境变量未正确配置：托管平台未配置MAILGUN_API_KEY或配置值错误，导致Mailgun鉴权失败
• 出站请求被拦截：A2托管封禁了Mailgun API所需的出站端口，或服务器IP未加入Mailgun白名单，请求被拦截
• Node.js版本不匹配：托管平台Node.js版本低于本地版本，高版本专属语法在低环境下抛出错误阻塞流程
• 依赖未正常安装：部署过程中nodemailer、nodemailer-mailgun-transport等依赖包安装失败，模块加载异常
• Mailgun配置错误：代码中填写的Mailgun域名未完成验证，或API密钥权限不足

• 申请开通A2托管的服务器日志权限，Node.js运行时的console.log输出、错误堆栈都会记录在日志中，可直接查看邮件发送的返回结果或错误信息，和本地gitBash控制台的输出内容一致
• 打印并校验托管环境下的process.env.MAILGUN_API_KEY值，确认和本地配置一致
• 分别在本地和托管环境执行node -v命令，对比Node.js版本，确认托管环境版本支持代码中用到的所有语法特性
• 在托管环境中手动调用sendMail方法测试，查看是否有报错返回

问题已解决：通过服务器日志结合托管平台技术支持协助排查，确认根因为代码中使用了仅最新版Node.js支持的replaceAll()方法，托管环境的Node.js版本不支持该语法，抛出错误后阻塞了所有服务端处理流程，本地运行正常是因为本地使用的是最新版Node.js。

内容的提问来源于stack exchange，提问作者Kayla Alewine