Spam algorithms are garbage.
A newsletter I've been following for weeks, as well as a confirmation that I entered an event were sent right to the spam folder.
Since Thunderbird doesn't download spam, I had to actually go straight to Outlook and tell it "Hey this newsletter I've been subscribed to FOR GODDAMN WEEKS is not spam, you fucking moron."
I take it email services don't factor in whether the sender's address has sent to my email previously and just throws out stuff that remotely looks like a spam email without thinking about it.
I can't believe that I have to tell it "hey this thing for a contest isn't spam" when I swear it should be friggin' obvious.