[aertergaery]

Was there any form of verification, signature or otherwise, provided by yourself or a household member at the time of delivery?

None, the delivery guy simply inserted it into the letter slot without any form of communication.

Also, not that It will have a significant Impact on the SE, but Is the letterbox securely locked?

It's not a US-style outdoor compartment letterbox, but rather just a hole in my door. It is not locked at all, and I wouldn't be surprised if one could put their hand through.