Problem sending email to one client

[newebirl]

Not quite sure how to word this but here goes

I have a client that when I send them an email it gives me the message:
An error occurred while sending mail. The mail server responded: requested action not taken: mailbox unavailable or not local. Please check the message and try again. [/quote]

This happens if I send a new email or reply to one sent to me.
I have 10 domains on my VPS package (Including my own) and it only happens with this one client.

This client has there mail setup to point to there own windows server IP address. Its set like this in cp.blacknight and on the VPS package. All the other DNS Settings are the same as everyone else.

If I send them a mail from my google account they get it no problem????

Can anyone figure this out as I am totally stumped.

[blacknight]

Alan

It's probably something quite simple, but we'd need to check

Could you let support know the domain name etc., so that they can look into it further?

Michele

[newebirl]

Will do Michele