I think its probably a little too niche for a Postal configuration, Postal just sends email it is given and doesn't really want to edit whatever flows through it.

Postal doesn't have any mailboxes, as long as you're using a domain Postal knows about then it will allow it through.

I presume you're struggling with routes? With routes you can specify * so *@proxy.tech.net so it would route everything to the same destination.