Helpdesk WTF-ery

I'm having a problem with some email not showing up. I think it might be related to spam filters, either at my ISP, or with my domain which forwards email from my domain name to my ISP. I called my ISP first, who couldn't see anything wrong. They suggested I contact the folks who run the domain forwarding, since the problem has only arisen since a server failure a week or so ago which resulted in my not getting any mail at all for a day.

I called, and was told this was too complex for a mere help