Yes, There are two setting type global and local.
You can set the global settings for the plugin by going to Gravity Forms > Settings > Email Blacklist. There you can enter an email, comma separated list of emails or use a wildcard to block emails from a top level domain. As well as set a validation error message that the users will see. These settings will effect every form with an email filed.
Global Settings Image
Then there are the local settings. These are set on the forms email fields themselves under the Advanced settings tab. email, comma separated list of emails or use a wildcard to block emails from a top level domain. As well as set a validation error message that the users will see. These settings will effect every form with an email filed. These settings will override the global settings.
Local Settings
This means you can leave the global setting blank and only use the local settings. Or set global settings and then override them on a form email field level.
Please reference the Screen Shots from the main plugin page here
Hopefully this helps. Please let us know if you have any other questions.
