Contact form not working

[BJH]

Hi

When customers use the Contact form thay are presented with the following message after clicking Send.

Error returned from SMTP server (4: sorry, that domain isn't in my list of allowed rcpthosts (#5.5.3 - chkuser) )

Please wait for your browser to forward you to the next page or click here.

The site URL is www.spmodels.co.uk. I don't know where to begin looking on this one. Anyone seen it before or know what it means.

Regards

[wjcampbe]

This has been answered before - try a search across all boards, using

Error returned from SMTP server

as your search string.