Exchange email problem?

Ok, my client can send email just fine but when i try and send to them i get the following error:

Failed to deliver to %26#039;administrator@DOMAIN.co.uk%26#039;

SMTP module(domain DOMAIN.co.uk) reports:

host mxav1.DOMAIN.co.uk says:

550 %26lt;administrator@DOMAIN.co.uk%26gt; recipient rejected

can%26#039;t find anything on google, any ideas?

Cheers

Exchange email problem?

have you tried clicking the reply button instead of sending the whole thing? oh. Are you using yahoo to send or Microsoft Outlook/Thunderbird? If you are using Outlook, maybe try to send the guy using yahoo.