Proof of postage

Hello there,

A parcel has been sent to me a few weeks ago and I haven't received it yet.
I am writing an email to the sender saying

'would you be able to send a proof of postage OF the parcel?)

Do I say of /to/for?

Many thanks
Anna

[woodhouse]

Dear Anna,
I`m Mick...so a good idea might be to include the following sentence: I would be grateful if you could send me the proof of postage for the parcel that was sent, so that I can instigate a search with my postal authorities.
Mick