Images are one of the biggest performance factors in email: a single oversized image can spike your bounce rate, trigger spam filters, or cause your email to take 10 seconds to load on mobile. This guide covers everything you need to optimize them properly.
Unlike websites — where the browser can lazy-load images in the background — email clients are far less forgiving. Heavy images in emails create real problems:
The standard desktop email width is 600 pixels. Wider images get scaled down by most clients, so sending a 1200 px image only doubles the weight without improving perceived quality.
Practical rule: each image in your email should weigh less than 100 KB. A hero header image can reach 150–200 KB if it's the primary visual element, but everything else should stay under 80 KB.
| Format | Email support | File size | When to use |
|---|---|---|---|
| JPG | ✅ Universal | Small | Photos, hero images, banners |
| PNG | ✅ Universal | Larger | Logos with transparency, icons, text on image |
| WebP | ⚠️ Partial | Very small | Only if your platform supports it with fallback |
| GIF | ✅ Universal | Variable | Simple animations |
WebP in email has partial support: Gmail (web) and Apple Mail render it fine, but Outlook (all desktop versions) does not support it. Unless your platform automatically handles the fallback, the safest choice is JPG for photos and PNG for graphics with transparency.
When an email client blocks images, recipients see the alt attribute. Descriptive alt text keeps your message readable. Instead of alt="", use alt="Exclusive offer: 30% off all courses this weekend".
Spam filters penalize emails where all content is a single image. Maintain at least a 60% text / 40% image ratio. Text also shows up better in email preview snippets in the inbox.
Embedding images in Base64 directly in the HTML dramatically increases email size and triggers spam filters. Host images on your server or CDN and reference them with absolute URLs.
Defining dimensions in the code prevents layout jumps while images load — especially important on mobile: <img src="banner.jpg" width="600" height="300" alt="...">.
Recommended workflow before inserting an image into your email:
ComprimirPro reduces your image weight by up to 80% in seconds, directly in your browser. No file uploads to any server.
⚡ Compress images free| Platform | Attachment limit | Notes |
|---|---|---|
| Mailchimp | 10 MB per email | Recommends images under 1 MB each |
| Brevo (ex-Sendinblue) | 5 MB total | Compress before uploading |
| ActiveCampaign | No strict limit | Recommends <600 KB total HTML |
| HubSpot | No strict limit | Images automatically served via CDN |
| Gmail personal | Clipping at 102 KB HTML total | Not a marketing platform, but applies to campaigns |
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