sendgrid/docs — pull request #487 by scottkawai (2014-07-10 15:28:58+00:00)
Title: 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.