Proof is only necessary if your giftee reports No Gift and it is not guaranteed to be looked at before then. If there has been a No Gift report, your proof will go into the queue to be reviewed.
Every single proof of shipping submitted to us is hand reviewed by a human. Unfortunately, this can sometimes create a backlog of shipping proofs during very busy exchange times. We will review yours in the order it was received and you will receive an email once it is accepted or you will be emailed if your proof can not be accepted as originally submitted.
Although we do ask that everyone retain proof of shipping until after their giftee confirms receiving a gift, submitting proof of shipping is optional while marking your gift shipped is mandatory. Once your giftee confirms receiving your gift in the gallery, proof of shipping is not necessary and will not be reviewed.
However, if your giftee is slow to confirm receiving their gift or the delivery time is longer than most, any backlog of shipping proofs will not cause account issues for you. Shipping proofs where a no gift report has been made will receive top priority.