I can see it has already been explained in this Q&A forum that lui is never changed to l', which is good to know.
My question is, I have seen envoyer in a list of 'verbs without prepositions' on another section of this website. I took that to mean it does not require à after envoyer, is this correct?
Is it because une message is added that it does require an à and therefore it becomes je lui envoye rather than je l'envoye?
I'm not sure how I should know whether envoyer requires le/la/les vs lui/leur?