Email Error: "User unknown in virtual alias table"

Starting this morning all emails sent to my clients’ email addresses are getting bounced with the following error:

“User unknown in virtual alias table”

I’m using the basic default settings for all email (i.e. no Custom MX or external SPAM filters in place, just the basic default email servers recommended by Dreamhost).

Users can send email without issue. Anyone else having trouble?

Here is the full text of the error message:

This is the mail system at host

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

If you are a current customer of DreamHost, please contact our
technical support team here

If you are not a customer please use our contact form at.

If you do so, please include this email in your support ticket. You can
delete your own text from the attached returned message.

           Dreamhost Email Support

<>: User unknown in virtual alias table

Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; User unknown in virtual alias table[hr]

I opened at trouble ticket over 4 hours ago and still no response from Dreamhost Tech Support. Typically these guys are great when something breaks, but this lack of any response is testing my patience. My clients are growing extremely frustrated with no update from Dreamhost and ignored request for a call back.