Some ESPs like Gmail and Libero clip emails that exceed a certain message size. In all cases where the message is larger than 102kb, the full content will be hidden behind a View entire message link. This limit is set at 102kb for Gmail e 80kb for Libero.
As shown in the image above the clipping includes text, the full URLs and tracking code of any links, the HTML used to style your content, and more. Each letter or character of the code is approximately 1 to 2 bytes. The total byte size of every character in the code creates the message size.
Mailup allows to verify the message size in any time in the Checkup page (Messages > Email > Saved > Checkup > Summary)
Alert me if the email that I am about to send exceeds (kB)
You can modify the message size limit in Settings > List settings > Preferences > Properties.
For some tips for streamlining your email and preventing clipping, read this blog post.