SMTPAPI Filters use "enable"

Toggling filters on and off is done with the `enable` key, not `enabled`.

If an `enable` key isn't present, the SMTPAPI assumes you're trying to enable it, and turns it on. This is why `enabled` will work when trying to turn on an app that is normally off, but will not work when trying to turn off an app that is normally on.
Merge pull request #487 from scottkawai/patch-1

SMTPAPI Filters use "enable"