So some of you (I estimate in the thousands) did not receive an email when they signed up. I presumed it was a mistake in my code, but I couldn't find anything wrong with it. Then vaypurist sent me a link to an FAQ page of my webhost, which explained that accounts are only allowed to send up to 1000 emails per hour via PHP. Presumably this is to stop spambots, and I've been told that this isn't uncommon practice amongst web hosts - it's just unfortunate that we were the victim.
Therefore, I am going to have to reset those members who signed up yet did not receive an email, along with those who have not yet confirmed their entry. Then I will keep an eye on how many people registered per hour, and close down submissions until the hour is over. I think we're over the initial peak, with entries increasing from 1000 to 8000 in 7 hours, so it shouldn't come to temporarily closing submissions, but we will see. I will put an announcement on the top of /r/trees when I reset the unconfirmed entries.
My apologies for this inconvenience, and good luck in the draw!
EDIT: If you never received an email, you must now sign up again.