Reply/Incoming mail bouncing

I have recently set up an account. Outgoing mail works fine but when anyone tries to reply or send mail to the address they get the following error message:

p3plibsmtp03-06.prod.phx3.secureserver.net rejected your message to the following email addresses:

mail@urbandynamics.com.au (mail@urbandynamics.com.au)
The email address wasn't found at the destination domain. It might be misspelled or it might not exist any longer. Try retyping the address and resending the message.

If that doesn't work, contact the recipient (by phone or instant messaging, for example) to check that the address is correct. If the problem continues, forward this message to your email admin.

For Email Administrators
For more tips to help fix this issue, see DSN 5.1.1 Errors in Exchange Online and Office 365.

p3plibsmtp03-06.prod.phx3.secureserver.net gave this error:
<mail@urbandynamics.com.au> Recipient not found. <http://x.co/irbounce>

Can anyone advise? MX records appear to be in order.

Thanks.