The Ninja Forms core (free) plugin needs to be installed, as well as Jetpack or the Akismet solo plugin to see the features mentioned in this this documentation. For detailed Akismet setup instructions click here.
Navigate to the Emails & Actions tab then select, Add new Action
Select the Akismet action.
In opening/editing the action, you can rename the Akismet action by changing the Action Name.
Upon editing the action you can utilize the merge tag feature to assign Akismet to monitor chosen fields for email spam. You can merge Name, Email, URL, and Message to Akismet monitoring.
Once finished, press the Done button in the top right hand corner of the form builder. Don’t forget to Publish any changes you wish to be saved.
Actions can be enabled or disabled using the toggles from the Emails and Actions tab of the builder.