Get the best email performance by following these image requirements when uploading to ContactMonkey.
Required Specifications
Requirement |
Specification |
Why This Matters |
File Size |
Maximum 1MB |
Images over 1MB may fail to load or load slowly, affecting recipient experience |
File Type |
PNG or JPG only |
These formats are universally supported across email clients |
Dimensions |
600-650px wide |
Optimal for both mobile and desktop viewing without scrolling |
Resolution |
72 PPI |
Ensures clear images without slowing load times |
File Type Guidelines
- PNG: Best for logos, graphics with transparency, and images requiring crisp edges
- JPG: Best for photographs and images with many colors
- SVG: Not supported
- WebP: Not supported
Before You Upload
- Compress large images using tools like TinyPNG before uploading
- Use image editing software to resize images to the recommended dimensions
- Test your images across different devices after uploading
Testing Images Before You Send
You can experiment with widths outside the recommended 600-650px range. If you do, test the email across multiple devices, email clients, apps, and browsers before you send.
Testing catches the most common problem with oversized images: a horizontal scroll bar appearing when recipients open your email. Your email should load correctly on every screen without the recipient needing to scroll sideways or zoom.
What to Test On
- Desktop and mobile devices
- Multiple email clients (Outlook, Gmail, Apple Mail)
- Mobile apps and web browsers
Send a test email to yourself and open it on each device type rather than relying on preview alone.
Sizing Headers and Footers
Match your header image width to your email's content area width. This gives you a 1:1 view, so the image displays at its intended size instead of being scaled up or down.
Find Your Content Area Width
- Open your draft in the Email Builder
- Click the Settings tab
- Check the Content area width value and update it if needed
- Use this number as the width for your desktop header image
For height, consider your overall file size in MB and the amount of copy you plan to include.
How Image Width Affects Legibility
To show the difference width makes, we created three header images at 1500x170px, 800x170px, and 400x170px. All three use the same height and the same title font size.
On Desktop
- 1500px: Scales down to fit the content area, so the text becomes small and hard to read
- 800px: Displays at 1:1 and looks correct
- 400px: Too narrow to cover the full content area width
On Mobile
- 1500px: Far too narrow to read
- 800px: Still narrow, and legibility drops further when the header contains more text
- 400px: Displays well and stays legible
No single width works well on both. For the best result on every device, use a double header.
How to Set Up a Double Header
A double header uses two images: one designed for desktop and hidden on mobile, and one designed for mobile and hidden on desktop. Recipients only ever see the version built for their device.
- Upload each header image to its own row
- Select the first row
- In the properties menu on the right, find the Hide on setting
- Select the device you want to hide that row on
- Repeat for the second row, hiding it on the opposite device
How to Confirm a Row Is Hidden
Switch between desktop and mobile mode using the toggle on the top left. A blurred image means that row is hidden in the mode you're viewing. The Hide on setting in the row's properties menu confirms which device it's hidden on.
Blurred images never appear in test or sent emails. Recipients only see the header image intended for their device.
Desktop mode: The blurriness of an image below indicates that it is hidden on the desktop. The Hide on setting in the row's properties menu confirms it.
Mobile mode: The blurriness of an image below indicates that it is hidden on mobile. The Hide on setting in the row's properties menu confirms it.
