As goofy as it sounds it is a security step that was taken so spammers could be weeded out.
Since a viable email needs to be entered to get access Spammers needed to enter a legit email. being able to change your email before actually posting means we would be stopping the wrong addresses.
Note: this forum also shares spam info with other forums using SMF forum software. this includes IP addresses as well as email addresses.
Once a spammers info is entered into the black list it is there permanently.