Introduction
The weight of an image plays an essential role in the reading experience of your emails. An image that's too heavy can slow down the loading of the email, or even prevent it from being displayed, especially on mobile or in the event of a slow connection. This can affect the perception of your message, subscriber satisfaction... and even your deliverability rate. Ideally, an image should not exceed 1 MB.
Why is the weight of an image so important?
When a recipient opens your email, all external resources - including images - are downloaded in real time. If an image is too heavy:
- it will take longer to display (if at all),
- it will slow down the overall loading of the email,
- it may be blocked by some mailboxes or firewalls,
- it will consume data unnecessarily, especially on mobile.
- Environmental impact is greater
A well-optimized image improves the user experience, but also the performance of your campaigns.
| Format | Ideal weight |
Note |
PNG |
< 500ko |
Ideal for logos and transparent elements (adaptable background, dark mode) |
JPG |
< 500ko |
Ideal for full-screen photos & visuals, reduced weight. |
GIF |
< 1MB |
Ideal for making animation |
Good practices
- Prefer JPEG or PNG format depending on the type of image (photo vs visual with transparency).
- Avoid unnecessary images: every image counts.
- Compress your files before integration.
- Beware of GIFs: animated, they can very quickly exceed 2 MB if not optimized.
Conclusion
Controlled weight guarantees a better reading experience, better deliverability and better display on all media. Systematically check your files before sending, and compress them as soon as necessary - it's a small gesture that can make a big difference to your campaigns.