Try registering test account with email address they provide here.
That site will accept any email sent regardless of issues it may have. If they receive it they will analyze it. Email being sent and going into black hole is usually the result of bad reverse DNS, if that is listed you need to contact your host.
If they don't receive it then it's server side issue.
“Results! Why, man, I have gotten a lot of results! I have found several thousand things that won’t work.”
Attributed - Thomas Edison