Delivery to the following recipient failed permanently:

[bigmaz]

Hi

We are having problems with one of our email addresses. This is the error we get when trying to send an email:

Delivery to the following recipient failed permanently:

(email address removed)

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550-Verification failed for

Any ideas? We know the address exists, as we can send email to it from other addresses....

Regards
Martin