Hi Diane,

As is said in this lesson, the verb 'envoyer' doesn't follow this pattern and it is:

'j'enverrai, tu enverras..."

Take a look at the following Kwiziq lesson for the details -

https://progress.lawlessfrench.com/revision/grammar/conjugate-voir-and-envoyer-in-le-futur-future-tense

I don't believe this has ever been different, you will hear young children saying 'jenvoierai' which is known as a 'logical error' when French children are following the grammatical rules unconsciously but not the exceptions until they are much older. ( like faisez and not faîtes, disez and not dîtes)  

Hope this helps!