LIve Mail not getting some e-mail

My wife has been having problems getting a newsletter from a site. DirtDoctor.com. It's the only site that she has a problem with.  The site keeps telling her to look in her spam/junk folder but nothing shows up either in her spam/junk folder or her inbox. She did get an e-mail response from the moderator about looking in her spam/junk folder but that's the only item she's received. I've been looking everywhere but I can't find that she's ever received any of the weekly newsletters and I'm wondering if there's anything that could be blocking from this 1 source.  I did check her blocked sender list and they're not in there.  Hope someone has a suggestion.  Thanks