Implement the ability to add arbitrary headers to emails sent via mod-email. For a description of one particular usecase see
Custom headers are configured by creating entries in mod-configuration with following (required) properties:
Where HEADER_NAME_HERE should be replaced with the name of your custom header, e.g. X-SES-CONFIGURATION-SET, and HEADER_VALUE_HERE should be replaced with desired value.
Values of properties module and configName should not be changed, and are required in order to be discovered by mod-email and treated as custom header configurations.
You can configure as many custom headers as you want as long as they have different code values.