If you're still reading this: could you please allow + in the e-mail address?
I understand why you want me to sign up, but I have no idea how much e-mail you're going to decide to send me, and sending it to a plus-address allows me to filter it on my terms.
There's really no reason not to allow the + sign, unless you're going to do something nefarious with my e-mail address and you don't want me to know it was you.
How would plus-addressing prevent them doing something nefarious? I would think that if they're selling it, they could strip out anything post-plus in the process easily.
I understand why you want me to sign up, but I have no idea how much e-mail you're going to decide to send me, and sending it to a plus-address allows me to filter it on my terms.
There's really no reason not to allow the + sign, unless you're going to do something nefarious with my e-mail address and you don't want me to know it was you.