I forgot to commit to the recently launched Software Recommendations proposal thus I shouldn't be able to see the site or any questions/answers on it, than why I was able to open this question?
I also tried other questions, but this was the only one that revealed itself.
Looks like there is a problem around the emails tag because I can see content in these links too:
https://softwarerecs.stackexchange.com/questions/tagged/emails
https://softwarerecs.stackexchange.com/tags/emails/info
There is a fairly recent change which allows anyone to access the site via the Area 51 Visit the site now! link. (The Visit! button does not work, however.) But you should still be required to sign in. I verified with an incognito window that the question you linked to and the email pages are visible, but other pages are not.
While this is a strange hole, it doesn't seem to really be hurting anything. I'll mention it to a developer to see if it's easy to fix. If it's not... well, I guess you can enjoy that one question for the life of the private beta. ;-)
