Strange subscribe behavior

I use a form to allow folks to sign up for my mailing lists. One user is having trouble using the form and I think it might be a problem with smartlist. Whenever he sends a subscribe request, the following error is generated: X-Diagnostic: Mail coming from a daemon, ignored The domain of the address generating this problem is "@ib.sc.vu.lt" Could it be that smartlist doesn't know how to handle such a domain? Thanks, irwin