Registration blocked by Yahoo spam filter
I just registered for Zimbra forums. Then I started waiting for the registration confirmation so I could post a few 'feature reports' before the beta ends. A full quarter of Giants football later no email. Time to check the spam filter. Sure enough, the Yahoo mail filter put the 'click this link to complete registration' email into the spam file.
Now I can see how this might seem like spam, and I know I don't want to 'click this link' blindly. But you would think the spam filter could confirm that the link is going to another Yahoo company.
That said, I like my new desktop email client. Now to those feature reports ...