I have not received a confirmation from Sheffield that they've received my documents (aka a giant box). I did however get a reminder email to post my documents! (I have copied and pasted the email without personal info below). I realize that the process takes a while even if one has paid for priority service (due to quantity as well as the weather!) but hoping I get a generic "received" response soon.
You've already received it. The 'post your documents' email IS your confirmation from Sheffield that they have received it.
In most countries, you submit your application in person and then your sponsor mails their documents separately, but in the US, everything is sent together. Therefore, when you get the email to 'post your documents' that's actually your confirmation that they have received your documents.
However, you sent a giant box?! Generally, if the package is more than 1-2 inches thick and weighs more than about 2-3 lbs, you've probably sent too much
.
But, as long as you have included all the required documents, you'll be fine, but it may take longer for them to go through all your documents in order to process the visa, as they'll need to wade through all the extra stuff to get to the required documents (the only concern would be if they miss something important because it's hidden amongst all the unimportant documents).