---
title: "Email Customization - Headers, Templates & Tracking | OutboundSMTP"
description: "Customize every aspect of your email sending: MAIL FROM domains per subaccount, custom headers, FROM addresses, templates, tracking pixels, and API-driven configuration."
image: "https://outboundsmtp.com/images/og-default.png"
canonical: "https://outboundsmtp.com/features/customization/"
---

# Total Email Customization 

Control every detail of your email sending -- from envelope headers to tracking pixels, across every sub-account.

[ Try 1000 Free Credits → ](https://insight.iljmp.com/4/smtp-free) 

Per-Subaccount Domains 

## Unique MAIL FROM per sub-account

Assign different MAIL FROM domains to each sub-account. Isolate reputation, brand each stream independently, and achieve DMARC alignment per application.

### Domain Isolation

Each sub-account uses its own MAIL FROM domain, so reputation issues in one stream never affect another.

### Brand Separation

Operate multiple brands or products from a single account while maintaining independent email identities for each.

### Independent Authentication

Each domain gets its own DKIM keys, SPF configuration, and DMARC alignment -- fully independent per sub-account.

Email Content 

## Customize every message

### Custom Headers

Add custom X-Headers to your messages for tracking, categorization, and metadata. Use headers to control delivery behavior and integrate with your analytics.

### FROM Address Management

Set different FROM addresses per message or per sub-account. Map multiple sender addresses to a single account for flexible multi-brand sending.

### Template Variables

Use merge tags in your SMTP messages for dynamic personalization. Replace variables at send time for recipient name, company, and custom fields.

### Tracking Controls

Enable or disable open tracking and click tracking per message. Customize tracking domains to match your brand and avoid third-party URLs.

API Customization 

## Programmatic control over everything

### Domain Management API

Add, verify, and configure sending domains programmatically. Automate domain setup for new clients or applications.

### Webhook Configuration

Set up and manage event webhooks per sub-account via API. Each application can receive its own delivery, bounce, and engagement events.

### Sending Rules

Define sending rules and policies per sub-account via API. Set rate limits, allowed recipients, content filters, and delivery windows.

FAQ 

## Customization questions

### How many MAIL FROM domains can I configure?

There is no limit on the number of MAIL FROM domains. Each sub-account can have its own domain, and you can add as many sending domains as your setup requires.

### Can I customize tracking domains?

Yes. You can set a custom tracking domain (e.g., track.yourdomain.com) so that open and click tracking links use your brand instead of a third-party URL. This also improves deliverability.

### Are template variables available via SMTP and API?

Yes. Template variables work across both SMTP (via X-Headers) and the RESTful API. You can define variables in your message content and pass values at send time for dynamic personalization.

## Make it yours

Full customization included with every plan. Start with 1,000 free credits.

[Try 1000 Free Credits→](https://insight.iljmp.com/4/smtp-free)[Schedule a Demo](/contact-us/)

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```

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```