Mail-Enabled Public Folder: Email being received by one address but not another

Hello all,

I have a Mail-Enabled public folder that has two email addresses associated with it. For purposes of this discussion I'll call them AddressOG (original) and AddressNew (new domain).

The public folder is set up to accept messages from all senders and block messages from none. AddressNew is set up as the default reply address.

When external users send an email to AddressNew, they get a failed delivery notice stating something along the lines of "the address could not be found." When they send to AddressOG, the mail gets delivered without issue.

Both addresses are associated with the same public folder, so I'm struggling to find why mail would fail to one but not the other.

Any insight?