Case sensitive free emails

[thetomcake]

Hi Dave,

I noticed some free emails getting through our filter and could not figure out how it was happening until I started logging the data of the requests.

Turns out [e-mail] == free but [e-mail] == not free. I can't see this on the docs and wasn't sure if this was deliberate or not?

Screenshot:

Happy to provide a PR if this is incidental, just wanted to confirm first.