Too large to translate

I upgraded to version 7 so I could use the translate feature.
But the mails I want to translate are “too large to translate”.
The mails are from job sites so they are not small, but also not massive.
I can’t say exactly how big as EMC doesn’t seem to tell me.
What’s that about? Why can’t they just be translated a bit at a time?
This is the sole reason I upgraded.
Is there another way this can be done?
If it were just a case of copying the text into a browser I would do it, unfortunately it is formatted html so not that straightforward.