Sometimes if you use gmail or certain other email service providers, they truncate the email if it gets too long.
(And sometimes we send long emails out with lots of great content.)
If your email has been cut off half way, there is usually a button at the end of the email that allows you to download the rest of the email.
In Gmail, it usually comes in the form of a link such as "read the rest of this email".
This process of truncating emails is entirely up to your email service provider.