SMTP vs Email API: Which Should You Use?

S: 220 smtp.example.com ESMTP Postfix
C: EHLO myapp.example.com
S: 250-smtp.example.com
S: 250-AUTH LOGIN PLAIN
S: 250 STARTTLS
C: STARTTLS
S: 220 Go ahead
C: AUTH PLAIN [base64 credentials]
S: 235 Authentication successful
C: MAIL FROM:<[email protected]>
S: 250 Ok
C: RCPT TO:<[email protected]>
S: 250 Ok
C: DATA
S: 354 End data with <CR><LF>.<CR><LF>
C: From: [email protected]
C: To: [email protected]
C: Subject: Welcome!
C:
C: Hello, welcome to the app.
C: .
S: 250 Ok: queued as 12345
C: QUIT

POST https://api.tinysend.co/v1/emails
Authorization: Bearer ts_live_your_api_key
Content-Type: application/json

{
  "from": "[email protected]",
  "to": "[email protected]",
  "subject": "Welcome!",
  "html": "<h1>Welcome</h1><p>Hello, welcome to the app.</p>",
  "text": "Welcome to the app."
}

// Response (200 OK)
{
  "id": "email_01HXYZ...",
  "status": "queued"
}

import nodemailer from 'nodemailer'

// Create a transport — this manages the SMTP connection pool
const transport = nodemailer.createTransport({
  host: 'smtp.mailprovider.com',
  port: 587,
  secure: false, // true for 465, false for 587
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
  pool: true,      // keep connections open
  maxConnections: 5,
  maxMessages: 100,
})

// Send a password reset email
async function sendPasswordReset(userEmail, resetToken) {
  const resetUrl = `https://myapp.com/reset?token=${resetToken}`

  const result = await transport.sendMail({
    from: '"My App" <[email protected]>',
    to: userEmail,
    subject: 'Reset your password',
    text: `Click here to reset your password: ${resetUrl}`,
    html: `<p>Click <a href="${resetUrl}">here</a> to reset your password.</p>`,
  })

  // result.messageId is a local ID — no guarantee of delivery
  console.log('Queued:', result.messageId)
  return result
}

// Error handling — SMTP codes you need to know
// 421: Service temporarily unavailable — retry later
// 450: Mailbox temporarily unavailable
// 550: Mailbox unavailable (hard bounce) — remove from list
// 552: Message too large

// No library needed — just native fetch (Node 18+)
async function sendPasswordReset(userEmail, resetToken) {
  const resetUrl = `https://myapp.com/reset?token=${resetToken}`

  const response = await fetch('https://api.tinysend.co/v1/emails', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.TINYSEND_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      from: '[email protected]',
      to: userEmail,
      subject: 'Reset your password',
      text: `Click here to reset your password: ${resetUrl}`,
      html: `<p>Click <a href="${resetUrl}">here</a> to reset your password.</p>`,
    }),
  })

  if (!response.ok) {
    const error = await response.json()
    // HTTP 400: invalid payload (your bug)
    // HTTP 422: unprocessable — bad email address etc.
    // HTTP 429: rate limited — check Retry-After header
    // HTTP 5xx: service issue — safe to retry
    throw new Error(`Email send failed: ${error.message}`)
  }

  const { id, status } = await response.json()
  console.log(`Email ${id} — status: ${status}`) // "queued" or "sent"
  return id
}

// With templates, your app code is tiny — no HTML in JS
const response = await fetch('https://api.tinysend.co/v1/emails', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${process.env.TINYSEND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from: '[email protected]',
    to: userEmail,
    template: 'password-reset',
    variables: {
      firstName: user.name,
      resetUrl: `https://myapp.com/reset?token=${token}`,
      expiresIn: '24 hours',
    },
  }),
})

await fetch('https://api.tinysend.co/v1/sequences/onboarding/enroll', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${process.env.TINYSEND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    contact: {
      email: user.email,
      firstName: user.name,
      plan: user.plan,
    },
    // Sequence handles: welcome → day 2 tip → day 7 check-in
    // Conditions evaluated server-side using contact properties
  }),
})