Testing Personalisation Before Sending

Personalised emails are powerful when they work correctly — and embarrassing when they do not. A recipient receiving "Hi {{first_name}}," or seeing their colleague's order details is a direct trust failure. This article covers a systematic testing approach for every type of personalisation, including the edge cases most teams miss.

The Personalisation Testing Framework

Test personalisation across four dimensions before any send:

1. Happy path — all variables provided correctly
2. Missing variables — one or more variables absent; fallback values activate
3. Edge case values — unusual but valid values (very long names, special characters, zero amounts)
4. Conditional logic — test both true and false paths for every conditional block

Method 1 — Dashboard Preview with Sample Data

1. Open your template in the MigoSMTP editor.
2. Click Preview.
3. In the preview panel, enter sample variable values that represent each scenario you want to test.
4. Switch between scenarios using the preview variable inputs to verify each renders correctly.

This is the fastest first pass — catch literal {{variable}} rendering issues immediately before spending time on real test sends.

Method 2 — Test Email Send

Send test emails that represent each test scenario to a real inbox:

// Test Scenario 1 — All variables provided (happy path)
POST /v1/email/send
{
  "from": "test@yourcompany.com",
  "to":   "yourtestemail@yourcompany.com",
  "template_id": "order-confirmation-v2",
  "variables": {
    "first_name":    "Rahul",
    "order_id":      "ORD-TEST-001",
    "order_total":   "2,499.00",
    "currency":      "₹",
    "delivery_date": "15 June 2026",
    "is_premium":    "true",
    "tracking_url":  "https://yourcompany.com/track/test"
  }
}

// Test Scenario 2 — Missing first_name (fallback test)
POST /v1/email/send
{
  "from": "test@yourcompany.com",
  "to":   "yourtestemail@yourcompany.com",
  "template_id": "order-confirmation-v2",
  "variables": {
    "order_id":      "ORD-TEST-002",
    "order_total":   "3,199.00",
    "currency":      "₹",
    "delivery_date": "16 June 2026",
    "is_premium":    "false"
  }
  // first_name omitted — should show fallback "there"
}

// Test Scenario 3 — Edge case values
POST /v1/email/send
{
  "from": "test@yourcompany.com",
  "to":   "yourtestemail@yourcompany.com",
  "template_id": "order-confirmation-v2",
  "variables": {
    "first_name":    "Konstantinos-Alexandros",  // Very long name
    "order_id":      "ORD-TEST-003",
    "order_total":   "0.00",                     // Zero amount
    "currency":      "$",                        // International currency
    "delivery_date": "3 July 2026",
    "is_premium":    "true"
  }
}

Edge Cases to Always Test

Automated Pre-Send Personalisation Check

For production systems sending personalised transactional emails at high volume, automate the variable validation as part of your send pipeline:

// Node.js — Personalisation validation middleware
const TEMPLATE_REQUIRED_VARS = {
  'order-confirmation-v2': [
    'first_name', 'order_id', 'order_total', 'currency', 'tracking_url'
  ],
  'password-reset': ['first_name', 'reset_url', 'expiry_minutes'],
  'trial-expiry':   ['first_name', 'plan_name', 'days_remaining', 'upgrade_url'],
};

function validatePersonalisation(templateId, variables) {
  const required = TEMPLATE_REQUIRED_VARS[templateId] || [];
  const warnings = [];
  const errors   = [];

  for (const varName of required) {
    if (!variables[varName]) {
      if (['tracking_url', 'first_name'].includes(varName)) {
        // Non-critical — warn but do not block
        warnings.push(`Missing variable: ${varName} (fallback will be used)`);
      } else {
        // Critical — block the send
        errors.push(`Missing required variable: ${varName}`);
      }
    }
  }

  // Check for excessively long values
  for (const [key, value] of Object.entries(variables)) {
    if (typeof value === 'string' && value.length > 500) {
      warnings.push(`Variable ${key} is very long (${value.length} chars) — may affect layout`);
    }
  }

  return { valid: errors.length === 0, errors, warnings };
}

Personalisation Testing Checklist

Next Steps

• Introduction to merge tags
• Conditional content blocks
• Email preview & testing before sending