Apologies @ Im_Guilty, I did not see this until two years later. Not that I am really qualified to respond here, but here is one link:
We "submit" something for approval or to be processed, like an answer, a business proposal, our job application, or our information for a flight ticket.
We send things like letters/emails/SMS text messages, flowers, good wishes, packages. These do not really need approval, or processing.
One question regarding pronunciation:
The recording sounds like "El_ envi_ uma reposta"
Now should I practice reading it that way or should I still pronounce every single syllable?