I'm not sure how to contact you otherwise than this way. The rejection notice included this handy little blurb:

Diagnostic-Code: smtp; 554 5.7.1 Your mail could not be delivered because the
recipient is only accepting mail from specific email addresses. If you feel
you received this in error, please contact the recipient directly and ask
them to check their email settings.

Paul: Finally managed to find an address to get on the site Many thanks.