Slow-loading emails frustrate subscribers and hurt engagement. Emails larger than 100KB may be clipped by Gmail, hiding your call-to-action or unsubscribe link. Large image files and unoptimized HTML code slow load times, especially on mobile devices.

This guide shows you how to reduce email load time by optimizing images, minifying HTML code, and improving mobile performance.

Before You Begin

To check your current email size:
Send a test Email Campaign to yourself in Gmail. Open the email → Click the three dots (⋮) → Select Show original → Click Download Original to see your file size.

💡 Tip: Keep your total email size under 100KB to avoid Gmail clipping.

Why Email Load Time Matters

Email load time affects:

User experience: Slow-loading emails frustrate subscribers, especially on mobile.
Inbox placement: Emails larger than 100KB are clipped by Gmail. If your unsubscribe link is hidden, recipients may mark your email as spam.
Engagement: Faster emails load completely before subscribers lose interest.

Key factors that increase email size:

High-resolution images (above 72 DPI).
Too many images (each image = 1 server request).
Unminified HTML and CSS code.
CSS animations and complex media queries.

Optimize Images

Limit the Number of Images

Each image in your email is a separate server request. If you load 20 small images, that's 20 requests, which increases load time.

How to reduce image requests:

Combine multiple small images into one larger image (use image sprites).
Replace decorative images (bullets, dividers, icons) with styled text or CSS shapes.
Use a 60:40 text-to-image ratio (60% text, 40% images). For every image, include 2–4 sentences of text.

💬 Learn more: Optimize Email Content for Improved Deliverability.

Reduce Image File Size

Follow these steps to compress images without losing quality:

1. Save images for web

Use the "Save for Web" function in your image editor to reduce file size without reducing quality.

2. Export images at 72 DPI

To check an image's DPI:

Windows: Right-click the file → Select Properties → Details. Check Horizontal Resolution and Vertical Resolution.
Mac: Open the image → Select Tools → Adjust Size in the menu bar.

Exporting at 72 DPI keeps images sharp while reducing file size.

3. Resize stock photos

If you download a stock photo, open it in an image editor, and resave it at the desired quality and size.

4. Keep images uniform

Mobile devices won't automatically resize side-by-side images if their height and width don't match. Keeping images uniform prevents mobile stacking issues.

5. Choose the right format

JPG for photographs
PNG-8 for simple images (logos, icons)
PNG-24 for images with photographic elements

PNG files maintain the highest quality but increase email size. Use JPG when possible.

6. Use image optimization tools

Run your images through third-party optimization apps (like TinyPNG, ImageOptim, or Squoosh) to further reduce file size while maintaining quality.

Break Long Emails Into Sections

Instead of creating a single, long email, break it into sections using dividers (Line or Space blocks).

Why this helps: Dividers separate your email into smaller HTML sections, allowing email clients to render content progressively from top to bottom. This makes your email appear to load faster, even if the total size stays the same.

How to add dividers in Omnisend:

In the Email Builder, drag a Line or Space block between content sections.
Repeat every 2–3 content blocks.

Emails without dividers load as one large block, which increases perceived load time.

Minify HTML Code

If you use custom HTML or CSS, minification removes unnecessary characters (whitespace, comments, line breaks) from your HTML and CSS code without changing how it works. This reduces file size by 20–30%.

Why minify?

Reduces email size (helps avoid Gmail clipping).
Speeds up rendering in email clients.
Saves mobile data for subscribers.

How to minify:

Copy your HTML code.
Use a minification tool like HTMLMinifier or Email on Acid's HTML Compressor.
Paste the minified code into Omnisend's HTML content block.

💡 Tip: Crop unwanted white space in images using HTML positioning instead of adding white space to the image file itself.

Optimize for Mobile Devices

Mobile download speeds are slower than desktop. If you have a large mobile audience, optimizing for mobile is critical.

Mobile optimization tips:

Compress images specifically for mobile – Use tools like TinyPNG or Squoosh to create smaller versions of images for mobile.
Use visibility settings – Hide non-essential content (large images, banners) on mobile devices to reduce load time.

How to set visibility in Omnisend:

Click the content block you want to adjust.
Go to the Layout tab.
Scroll to Visibility on devices → Choose which devices should show the content block:
- All devices.
- Mobile devices only.
- Desktop devices only.

Test Your Email Load Speed

After optimizing your email, test it to confirm improvements.

How to test:

Check total email size in Gmail:
- Send a test Email Campaign to yourself in Gmail.
- Open the email → Click the three dots (⋮) → Select Show original.
- Click Download Original to see your file size. Keep it under 100KB.
Use email testing tools:
- Litmus or Email on Acid show load time previews across devices and email clients.
A/B test optimized vs. non-optimized emails:
- Create two versions of your Email Campaign: one with optimized images, one without.
- Use Omnisend's A/B Content Test to compare engagement metrics.

FAQ

What's an acceptable email size?
Keep your total email size under 100KB to avoid Gmail clipping. Emails larger than 100KB are truncated, and recipients must click "View entire message" to see the full content.

Will compressing images hurt quality?
No, if you use "Save for Web" at 72 DPI. This maintains visual quality while reducing file size by 40–60%.

Can I use GIFs in my emails?
Yes, but GIFs are larger than static images. If you use GIFs: