Creating HTML emails is just the start—ensuring it renders perfectly across inboxes, devices, and email clients is what separates a good emailer from a great one. While older tricks like pasting HTML into Outlook via the clipboard can work, they’re error-prone and outdated in today’s complex email landscape.

In this guide, we’ll walk you through a modern, reliable 6-step process to test and send emailers with confidence.

Why the Old Clipboard Method No Longer Cuts It

Some still copy HTML email content from a browser and paste it into Outlook. While this can embed visuals, it often results in:

• Broken layouts in Outlook due to its Word-based rendering engine

• Lost styles and non-responsive emails

• Missing or blocked images

• Inconsistent experiences across Gmail, Apple Mail, and mobile apps

It’s time to modernize.

Modern 6-Step Process to Test & Send HTML Emails

Prerequisites

• A well-designed HTML email

• Image assets hosted securely (e.g., CDN, ESP media library)

• Access to email testing tools (see tools list below)

Step 1: Build Your Email with a Professional Editor

Why this matters:
Hand-coding emails can be risky due to the inconsistent rendering engines used by email clients (especially Outlook). A professional email builder ensures your HTML is:

• Responsive (mobile-friendly)
• Inline styled (for older clients)
• Tested for compliance with major ESPs

Use a drag-and-drop email builder that outputs responsive and standards-compliant HTML:

• Stripo  – Supports AMP, dynamic content, and custom blocks
• BEE – Great UI, free to start, easy exports
• Mailchimp – Useful if you’re already using it as your ESP
• Unlayer – Developer-friendly embeddable editor

These tools allow:

• Device previews
• Export to HTML
• ESP integrations

Best Practice Tips:

• Start from tested templates
• Avoid external CSS—use inline styling
• Use <table>-based layout (still safest for compatibility)
• Include alt text for all images
• Keep the width within 600–800px for best rendering

Step 2: Test Email Rendering Across Clients

Why this matters:
Your email may look perfect in Gmail but break completely in Outlook. You need to test across dozens of environments to ensure consistency.

Use tools like:

• Litmus or Email on Acid – Test rendering across 100+ email clients and devices (Outlook 2016, Apple Mail, Android Gmail app, etc.)
• Mailtrap – test email delivery and spam score without hitting real users.
• PutsMail – Send real test HTML email to your inbox

What to check:

• Font rendering
• Line spacing and alignment
• Button size and CTA visibility
• Image display and scaling
• Mobile stacking and responsiveness

Step 3: Host Images Securely

Why this matters:
Embedded or base64 images might be blocked, inflate email size, or fail to load—especially in Gmail and Outlook. Properly hosted images ensure:

• Fast load times
• Reliable image rendering
• Trust (due to HTTPS URLs)

Avoid embedding images with base64 or CID unless absolutely necessary. Instead:

• Upload images to a CDN, ESP-hosted media folder, or your own secure HTTPS server.
• Use absolute image paths in your HTML (e.g., https://mydomain.com/assets/logo.png).

Pro Tips:

• Keep file sizes low (<200KB per image)
• Use modern formats like .webp if supported
• Optimize for retina displays (2x resolution if needed)

Step 4: Test Deliverability and Spam Score

Why this matters:
Your beautifully designed email won’t matter if it lands in spam. Spam filters look at your content, sender reputation, domain settings, and HTML quality.

Use:

• Mailtrap’s spam analysis – Test for spam scores and HTML compliance
• Google Postmaster Tools (for domain reputation) – Monitor sender reputation and bounce rates
• Send test via your ESP to check:
  • DKIM, SPF, and DMARC alignment
  • Inbox placement (not spam or promotions)

What to validate:

• SPF/DKIM/DMARC are properly set on your domain
• Subject line is not spammy (avoid “free”, “buy now”, “!!!”)
• Avoid too many links or large image-to-text ratios
• Test with seed list across Gmail, Outlook, Yahoo, etc.

Pro Tips:

• Always include an unsubscribe link
• Use a plain-text version alongside your HTML
• Avoid hidden text, base64, or obfuscated code

Step 5: Send Tests to Real Inboxes for Live Preview

Why this matters:
Even with rendering tests, nothing beats checking how it looks to real users. This ensures you’re catching issues with:

• Load times
• Email previews and snippets
• Display in light/dark modes
• Visual hierarchy and spacing

How to do it:

• Send test emails to yourself and team
• Check on multiple devices:
  • Gmail (Web, Android, iOS)
  • Outlook (Windows desktop + web + mobile)
  • Apple Mail (Mac + iPhone)
  • Yahoo, ProtonMail, others if relevant

What to observe:

• Subject line and preview text appearance
• CTA placement on mobile vs. desktop
• Clarity of images and fonts
• Tracking pixel loads (if you use analytics)

Pro Tip:
Use seed lists and A/B variants to test alternative subject lines or headers.

Step 6 (Optional): Save as Outlook .MSG File

Why this matters:
In some enterprise environments, marketing or compliance teams require an .MSG file preview before a bulk send—especially if Outlook is the dominant client.

If your company still requires Outlook .msg previews for internal approvals:

• Send email to yourself via Outlook

• Drag the email to desktop or Save As → .msg

This ensures stakeholders can preview the exact format.

Pro Tips:

• Make sure to test the .msg in different Outlook versions (some use Word-based rendering)
• Confirm images and formatting remain intact after saving
• Avoid sending actual test blasts to stakeholders—they may forward them and skew your metrics

Bonus Tips

• Keep subject lines clear and under 60 characters
• Always include an unsubscribe link (to comply with CAN-SPAM & GDPR)
• Avoid JavaScript, background videos, and form elements in email HTML