Open to other configuration opens for how best to make this optional. Or
potentially making this an opt in configuration item which would be a
breaking change.
The main reason that someone would want to disable this is if their raw
SPF record goes over the 255 characters. This is potentially another
place that could get some multi string support. But as it is only used
for debugging purposes it seems like there should be a way to outright
disable it too.
FYI: The support is very minimal. It only supports redirect if it is the last item in an SPF record. At that point, it is equivalent to include.
* In SFP, treat redirect like a special include.
* Document SPF redirect: limited implementation.
