For envelope items, I can use Australia Post registered post lodgement receipts at my post office.  I fill them out and the post office will stamp them.  I've used this for proof of post on a few occasions and these have always been decided in my favour.  Without the need for deliverey conformation.

https://auspost.com.au/media/documents/registered-post-lodgement-receipt.pdf

https://auspost.com.au/media/documents/registered-post-multiple-lodgement-document.pdf

I normally wouldn't leave feedback on these occasions (to limit green dots where not deserved) But I I do like your idea to comment INR in feedback. It would help make clear to other useres if someone was using one acount for many INR cases.