If your email exceeds 102KB in file size, Gmail will display the first 102KB along with the following message:
[Message clipped] View entire message
When a user clicks to view the entire message, your email will be displayed in a new window.
To reduce the file size of your email, remove any white spaces and compress your HTML. Additionally, you may need to remove some content or merge content together to further reduce the file size of your email.
Changing the file size of images, by reducing the quality or making them smaller, will not reduce the file size of the email. The file size of the email is based on the email’s code. As images are loaded into emails from an external source, such as from a server, the image size does not affect the size of the email.