I tried 2 different Yahoo.com email addresses and no account validation email ever made it to my inbox or even spam folders.... I was forced to use my work email to register here.
The 1990's called.
They want their email address back. 
(They also want this joke back.) 
...
Seriously, though, I recommend a Gmail account if you don't want to use your work account. 
Thanks for letting me know. Unfortunately integration with the diverse email system is insanely difficult to set up and even more difficult to debug, so I can’t do much at the moment besides recommend not using Yahoo.
As proof of how difficult it is to debug, I just signed up a test account with my Yahoo email address (from the 90’s I believe 
) and the account activation email arrived successfully. Also in the past couple of days we’ve have 10 or 15 new signups from Yahoo accounts. Go figure. :-/ I’m not doubting treysoucie’s report, but it just goes to show how incredibly arcane and complex the email system is, and especially Yahoo, I might add.