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Internet Service Providers (ISPs) like Gmail and Microsoft will usually clip large emails and download them slowly. Learn about email size and what’s recommended.
When an email client receives your HTML email there is a two-step process for rendering that email. First, the HTML is downloaded and rendered. Second, the images in the email are downloaded. This is why you will typically see the email load in two phases: HTML first, images second. The total size of the HTML and images combined results in how fast the email will be processed by the email client and on your device (desktop or mobile).
Generally speaking, optimal email size is:
- HTML code 125K or less.
- Individual image sizes 40K.
- If you have a large mobile audience, the smaller the total email size, the better.
In addition to helping your email load time, there are a few reasons why it is important to keep the total size of your email as low as possible.
Many email clients (especially mobile) truncate the email, cutting it off halfway through. You will see a “Download More” button in many cases.
ISP’s may block or "hold" large HTML emails for further examination. Large emails can be a sign of spam or an email carrying a virus or malware.
Example of a bounce back message indicating email is too large…
"Exceeded maximum inbound message size"
Mobile load time
With mobile opens between 60-70% it is more important than ever that your emails are as light as possible. Large images will download slowly and could even crash the email application on a mobile device. The easiest way to see if this is an issue is by testing your email on a mobile device.
The following tips will help you manage the size of your email, improve user experience and engagement, as well as inbox deliverability.
Create lighter emails using emails with fewer columns, concise text and more links off to your website for additional information. Use the correct image format (details below) and reduce the number and overall weight of images as much as possible.
When choosing your image formats, consider your options. The three most common formats are GIF, JPG, and PNG.
Good for small, low color images, as well as images that include text
Examples include logos and buttons, also animated images
Good for photos (especially ones with lots of color) and making smaller file sizes
Reduce 40% quality
Examples include hero images
Good for small images with transparency
Displays best on mobile
Examples include header images, logos, and images with text
You can find the size of your email in most email clients. But there's also an easy way to do this in your browser.
How to find the total weight - code + images - of your email using a browser:
1. Load the 'view email as webpage' link from your email in Chrome.
2. Right-click on the email and select 'Inspect'.
3. Select the Network tab from the inspector tools.
4. Reload the email in the browser tab.
5. The total weight in KB will appear at the bottom of the Network information.
Email code size in Outlook
In Outlook, find your email size under File > Info. Open the email you wish to review by double clicking on it, this should open it in a separate window. Click File on the top left corner, and then click the Info section. You will see a section titled Properties on the right. The email code size will be listed under Properties. This is the size of your email code, excluding images.