SMTP server setup: send website emails without spam

Emails sent from your website often land in spam. Customers may not receive order notifications. This situation is all too familiar. Most often, the cause is an incorrect SMTP server configuration or missing SPF/DKIM records. With 7+ years of experience and over 200 email delivery projects, we guarantee a 99.9% inbox delivery rate. In this article, we break down how to configure email sending via SMTP using Nodemailer, set up a connection pool for high load, and avoid delivery problems. A turnkey setup takes from 1 to 5 days depending on complexity. Save up to $500/month by switching to a properly configured SMTP relay. Typical monthly savings range from $200 to $1500 depending on volume. If you want a ready-made solution, contact us for a free project assessment.

Reasons emails end up in spam

There are three main reasons. First, missing SPF (Sender Policy Framework) record in DNS: the SMTP server is not authorized to send mail from your domain. Second, poor reputation of the IP address from which the emails are sent. Third, incorrect email headers (no DKIM signature, wrong From address). Even if you use a free SMTP (Gmail, Yandex), you must configure these three components. Otherwise, emails are guaranteed to go to Promotions or spam.

How we set up SMTP: a case from our practice

Recently, from our practice: we configured email sending for an e-commerce client with 10,000 transactional emails per day: order confirmations, invoices, delivery status updates. We used the Mailgun SMTP relay with the following parameters:

• Connection pool: 5 parallel connections, 100 messages per connection
• Queue with Bull and retry logic: 3 attempts with 30-second delay
• Full set of DNS records: SPF, DKIM, DMARC (quarantine policy)
• Monitoring of bounced emails via Mailgun webhooks

Result: Inbox delivery rate — 99.2% (compared to 40% before setup). This shows that proper configuration is 2.5x more effective. Sending costs reduced by 30% by switching from an expensive ESP service. Experience shows that proper SMTP configuration pays for itself within the first month.

Technology choice: Nodemailer vs third-party SDKs

Nodemailer is 2x faster to set up than integrating a separate SDK for each provider: one library covers all popular SMTP servers. SDKs from SendGrid or Mailgun tie you to a single provider. For flexibility, we use Nodemailer + Bull for queuing. For those using Postfix, configuration is similar but requires different port settings. Monitor blacklists daily to maintain sender reputation. Sending with a connection pool is 10x more efficient than sequential delivery.

Step 1: Sending via Nodemailer and connection pool

This guide shows you how to send email from website using SMTP. Nodemailer configuration is straightforward.

npm install nodemailer
npm install -D @types/nodemailer

import nodemailer from 'nodemailer';

const transporter = nodemailer.createTransport({
  host: process.env.SMTP_HOST,        // e.g., smtp.gmail.com, smtp.yandex.ru
  port: Number(process.env.SMTP_PORT ?? 465),
  secure: true,                        // true for 465, false for 587
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
  // For corporate SMTP with self-signed certificates
  tls: {
    rejectUnauthorized: process.env.NODE_ENV === 'production',
  },
});

// Verify connection on server start
await transporter.verify();
console.log('SMTP ready');

Sending an email

async function sendEmail(params: {
  to: string | string[];
  subject: string;
  html: string;
  text?: string;
  attachments?: nodemailer.Attachment[];
}) {
  const info = await transporter.sendMail({
    from: `"Acme Support" <[email protected]>`,
    to: params.to,
    subject: params.subject,
    html: params.html,
    text: params.text,
    attachments: params.attachments,
    headers: {
      'X-Mailer': 'Acme App v2',
    },
  });

  return info.messageId;
}

// Example with PDF attachment
await sendEmail({
  to: '[email protected]',
  subject: 'Your invoice #INV-2026-042',
  html: invoiceHtml,
  attachments: [
    {
      filename: 'invoice-2026-042.pdf',
      content: pdfBuffer,
      contentType: 'application/pdf',
    },
  ],
});

Connection pool for high load

SMTP connection pool increases throughput. When sending many emails, create a pool instead of a single transport:

const poolTransporter = nodemailer.createTransport({
  pool: true,
  maxConnections: 5,       // parallel connections
  maxMessages: 100,        // messages per connection before reconnection
  host: process.env.SMTP_HOST,
  port: 465,
  secure: true,
  auth: { user: process.env.SMTP_USER, pass: process.env.SMTP_PASS },
});

Step 2: How to set up DNS records for delivery?

DMARC SPF setup is crucial. Use email queue Bull for retries. For a detailed SMTP providers comparison, see the table below.

Step 3: Popular SMTP providers

Step 4: Testing in dev mode

SMTP testing with Mailtrap is recommended. For development, use Mailtrap or Ethereal — fake SMTP servers that intercept emails and display them in a web interface:

// Ethereal for local testing
if (process.env.NODE_ENV !== 'production') {
  const testAccount = await nodemailer.createTestAccount();
  transporter = nodemailer.createTransport({
    host: 'smtp.ethereal.email',
    port: 587,
    auth: {
      user: testAccount.user,
      pass: testAccount.pass,
    },
  });
}

Typical SMTP setup mistakes

• Missing SPF/DKIM/DMARC — emails go to spam
• Using free SMTP for commercial mailings — quick blocking
• No connection pool for loads >1000 emails/day — lost emails
• Ignoring bounce notifications — reputation drop
• Sending from an incorrect From address — emails rejected

What's included in turnkey setup

• Audit of current mail configuration
• Selection of optimal SMTP provider
• DNS configuration: SPF, DKIM, DMARC
• Nodemailer integration with pool and queue (Bull)
• Bounce monitoring and webhook setup
• Operations documentation
• Team training (1-hour online consultation)
• 99% delivery guarantee + 2 weeks support

Timelines

Nodemailer + SMTP + test environment setup — half a day. With Bull queue and retry logic — 1 day. Full cycle (analysis → design → implementation → test → deploy) — from 1 to 5 days depending on traffic volume. If you have questions about SMTP setup, contact us — we'll help. Free project assessment.

To avoid spam, ensure proper email delivery configuration. Implement blacklist protection measures.

Email Campaign Integration: Why Does It Often Break?

We’ve observed that a trigger email sent 10 minutes after registration converts 4–5 times better than the same email sent after 24 hours. This isn’t a marketing myth—it’s mechanics: while the user is still warm, while they remember the context. But most integrations with email services are built like this: form submits → synchronous HTTP request to API → if the API is slow, the user waits 3 seconds → the email either goes out or doesn’t, nobody knows. In one project, we saw a 30% drop in conversion simply because the email service responded with 504 and Laravel’s queue driver wasn’t configured. Lost emails often hit customers silently – no log, no alert, just a missing order confirmation.

If you’re facing lost emails or spam folder issues, order an audit of your current integration – we’ll find bottlenecks within 2 days.

Providers and Their APIs

Unisender — a Russian provider popular in the SMB segment. REST API, simple. Adding a contact: importContacts, sending a transactional email: sendEmail. Important: for transactional emails (order confirmations, password resets), Unisender Go is a separate service with a different API and separate pricing. Mixing bulk and transactional mailings in one stream is bad for domain reputation. Unisender Go handles up to 1000 requests per second.

SendPulse — provides email, SMS, web push, Viber, and Telegram bots through a unified API. Convenient for projects requiring an omnichannel approach. Automation 360 is a visual chain builder; you can trigger automation via API events. The PHP SDK (sendpulse/rest-api-php-sdk) is maintained but updated irregularly – better to use Guzzle directly.

Mailchimp — a choice for international audiences and marketing teams accustomed to the Mailchimp ecosystem. Transactional email via Mandrill (a subsidiary service). Marketing API v3 for list, tag, and campaign management. Webhooks for opens, clicks, unsubscribes, bounces.

SMS. For Russia: SMSCenter, MTS Exolve, Devino Telecom, SMS Aero. Their APIs are similar: a send method with phone, message, sender parameters (sender name must be registered separately with the operator). One nuance: the sender name must be registered through the aggregator with a contract – otherwise SMS won’t be sent on MTS/MegaFon/Beeline networks.

How to Build an Integration That Doesn’t Lose Emails?

Separate Transactional and Marketing Streams

Transactional emails (order confirmations, password resets, delivery status) go through a dedicated sender domain or subdomain tx.example.com. Marketing campaigns go through mail.example.com or news.example.com. If a marketing campaign receives many spam complaints, it should not affect the reputation of the transactional stream. According to SendGrid documentation, transactional messages should be sent through a dedicated IP pool to prevent cross-contamination.

Queue and Retry

Any call to the email API goes through a queue (Laravel Queue, Bull, Celery). If Unisender returns a 503, the job retries after 5 minutes, then 15, then 60. After 5 failed attempts, it goes to a dead letter queue with an alert. The user already received their 200 OK and knows nothing about the issue. This approach reduces bounce rate on projects to 0.5%.

Example Laravel job:

public function handle(): void
{
    try {
        $response = Http::post(config('services.unisender.email_url'), $this->params);
        if ($response->failed()) {
            $this->release(300); // retry after 5 min
        }
    } catch (\Throwable $e) {
        $this->release(300);
    }
}

Templates

We store templates in code (Blade, Twig, React Email), not in the provider’s interface. Reasons: versioning via Git, browser preview without sending, testability. For complex templates with dynamic content — react-email with export to HTML via @react-email/render.

Validation and Consent

Before adding a contact to a list — double opt-in (confirmation email). Store the confirmation timestamp in your own database. Upon unsubscription — synchronously unsubscribe both at the provider and in your database. Ignoring webhook unsubscriptions is a direct path to account suspension at the provider. All processes comply with Федеральный закон № 152-ФЗ «О персональных данных».

Deliverability Monitoring and DKIM Setup

Connect provider webhooks for events: bounce (hard and soft), spam_complaint, unsubscribe. Hard bounce — immediately mark the email as invalid in your database, stop sending. Soft bounce 3 times in a row — same. Metrics: open rate, click rate, bounce rate, unsubscribe rate — review at least once a week. Our certified engineers configure alerts in Grafana/Prometheus.

DKIM configuration steps:

1. Generate a key pair (e.g., openssl genrsa -out private.key 2048).
2. Publish the public key in DNS as a TXT record for the selector (e.g., mail._domainkey.tx.example.com).
3. Provide the selector to the provider (SendGrid, Mailgun, Unisender).
4. Verify with dig TXT mail._domainkey.tx.example.com.

SPF, DKIM, DMARC must be configured separately for each stream. We use subdomains with different DNS records.

Why Is It Important to Separate Streams?

If you send a marketing campaign from the same domain as transactional emails and receive spam complaints, you risk getting the domain blocked — and users will stop receiving even order confirmations. SPF, DKIM, DMARC (Sender Policy Framework, DomainKeys Identified Mail, Domain‑based Message Authentication, Reporting and Conformance) must be configured separately for each stream. In one project, a marketing blast with 12% spam complaints blocked the transactional domain for 48 hours — we had to re‑authenticate with Google and Yandex.

What Does the Integration Scope Include?

• Audit of current communication streams and domain reputation (SPF, DKIM, DMARC)
• Provider and schema selection: transactional vs marketing traffic
• Configuration of SPF, DKIM, DMARC DNS records
• Development of email templates (HTML + dynamic content)
• Backend integration via queues and API
• Webhook setup for deliverability and complaints
• Operations documentation and team training
• Deliverability guarantee and post‑launch support

We deliver production‑ready documentation, access to monitoring dashboards, and a handover session with your engineers. Our certified engineers provide a 30‑day post‑launch health check guarantee.

Timelines and Cost

Cost is calculated individually after audit. We provide turnkey service: from analysis to production monitoring. Contact us for a free engineer consultation — we’ll evaluate your project and give accurate timelines. Over 7 years of experience in email service integration, 50+ projects implemented. Order a free audit of your current integration and receive a report with recommendations and estimated savings.