There does not seem to be a way to private message the admin, so this must be a public post.
I tried registering with a Yahoo.com e-mail, but I never got the acknowlegement e-mail.
I tried again with a Comcast.net e-mail and succeeded.
It looks like Yahoo thinks your sites e-mail is spam, and blocking it.
The Yahoo e-mail showed up several hours after I successfully registered with the Comcast account, with a time stamp about an hour before the e-mail through Comcast.