Email Size Limits by Provider
Most email providers impose attachment size limits:
- Gmail — 25MB total attachment size
- Outlook — 20MB per message
- Yahoo Mail — 25MB total
- Apple Mail — 20MB (offers Mail Drop for larger files)
Keep in mind that base64 encoding increases file size by roughly 33%, so a 25MB limit means your raw attachments should stay under ~19MB.
Optimal Image Dimensions for Email
Email clients render images differently than browsers. Follow these dimension guidelines:
- Email body width: 600-700px maximum
- Full-width images: 600px wide
- Two-column images: 280-300px wide
- Retina displays: Create at 2x and set display size in HTML
Compression for Attachments
When sending photos as attachments, compress them to balance quality and size:
- Individual photos: Target 200-500KB each
- Multiple photos: Keep total under 10MB for reliability
- Documents with images: Compress the images before embedding
Use JPEG format at 75-80% quality for photos. This typically reduces a 5MB camera photo to under 500KB with minimal visible quality loss.
Images in Newsletters
For HTML emails and newsletters, image optimization is crucial for deliverability and rendering speed:
- Total email size including images should stay under 100KB for best deliverability
- Host images externally and reference them via URLs
- Always include alt text for accessibility and when images don't load
- Use inline CSS for image styling (many email clients strip head styles)
Quick Tips
- Resize before compressing — don't send a 4000px wide image at 10% quality
- Use PNG only for screenshots with text (JPEG artifacts are visible)
- Consider using a link to a cloud album for large photo collections
- Test your emails across different clients to verify image rendering