Authoritative domain unknown address error 550 'no such user here' for other addresses

I was administering an Exchange server for multiple email domains that was previously receiving forwards from various internet email hosts until the site had reliable internet with a static IP, updated the internet MX record, etc. Once that happened, we reconfigured the 'accepted domains' from 'External Relay' to Authoritative.

Unfortunately now all email is rejected when it's addressed to email addresses that are not that user's primary address:

5.1.0 - Unknown address error 550-'No Such User Here"'

So let's say I have employee John Smith with the following email addresses:

• john.smith@domain.com
• johns@domain.com
• smith.john@domain.com

With the previous configuration, John Smith would receive emails that match any of those three addresses. Since flipping over to Authoritative, he's only receiving the bolded primary address!

Any and all insight would be appreciated!