NestJS Nodemailer - Error: ESOCKET - connect (when sending email verification OTP)

I'm encountering an error (ESOCKET - connect) while trying to send an email verification OTP using Nodemailer in my NestJS application. I'm using Gmail's SMTP server for email delivery. Here's a breakdown of my setup:

Mailer Configuration (app.module)

MailerModule.forRootAsync({
  useFactory: (configService: ConfigService) => configService.get('mailer'),
  inject: [ConfigService],
}),

mailer.config

export default () => ({
  mailer: {
    transport: {
      host: process.env.MAIL_HOST,
      port: parseInt(process.env.MAIL_PORT),
      auth: {
        user: process.env.MAIL_USER,
        pass: process.env.MAIL_PASSWORD,
      },
    },
    defaults: {
      from: process.env.MAIL_FROM,
    },
  },
});

register-email.provider

import { ConflictException, Injectable } from '@nestjs/common';
import { FindOneByEmailProvider } from 'src/users/providers/find-one-by-email.provider';
// import { v4 as uuidv4 } from 'uuid';
import { MailerService } from '@nestjs-modules/mailer';
import { OtpProvider } from './otp.provider';
import { EmailDto } from '../dto/email.dto';

@Injectable()
export class RegisterEmailProvider {
    constructor(

        private readonly findOneByEmailProvider: FindOneByEmailProvider,
        private readonly otpProvider: OtpProvider,
        private readonly mailerService: MailerService,

    ) {
        // Set up a periodic task to clean up expired OTPs
        setInterval(() => this.otpProvider.cleanUpExpiredOtps(), 60 * 1000); // Run every minute
    }

    public async registerEmail(registerEmailDto: EmailDto) {
        const { email } = registerEmailDto;

        const existingUser = await this.findOneByEmailProvider.findOneByEmailProvider(email);
        if (existingUser && existingUser.isActive === true) {
            throw new ConflictException('Email already exists', {
                description: 'Email already exists',
                // cause: 'User already exists',
            });
        }

        // const otp = uuidv4().slice(0, 6); // Generate a 6-character OTP
        const otp = Math.floor(100000 + Math.random() * 900000).toString(); //numeric otp
        const expiresAt = Date.now() + 15 * 60 * 1000; // Set expiration time to 15 minutes from now

        this.otpProvider.setOtp(email, otp, expiresAt);

        console.log('OTP:', otp);

        // Send OTP via email
        try {
            await this.mailerService.sendMail({
                to: email,
                subject: 'Email Verification OTP',
                text: `Your OTP for email verification is: ${otp}`,
            });

            console.log('OTP sent to email');

            return { message: 'OTP sent to email' };
        } catch (error) {
            throw new ConflictException(error, 'Failed to send OTP email');
        }
    }
}

Error Message

{
    "errno": -4039,
    "code": "ESOCKET",
    "syscall": "connect",
    "address": "209.85.202.108",
    "port": 587,
    "command": "CONN"
}

Question

I'm getting this ESOCKET error when the register-email endpoint is hit. I've verified that my environment variables are set as follows:

# mailer configuration
MAIL_HOST=smtp.gmail.com
MAIL_PORT=587
MAIL_USER=my_email_account  
MAIL_PASSWORD='xxxx xxxx xxxx xxxx'            # my gmail application password
MAIL_FROM='"Sender" <[email protected]>'

What could be causing this issue, and how can I resolve it?