Other headers as determined by the user (optional).
This property can be set to a string of headers to be appended to the HTTP request headers created from other properties, like ContentType, From, and so on.
The headers must be of the format "header: value" as described in the HTTP specifications. Header lines should be separated by the carriage return and line feed (CRLF) characters.
Use this property with caution. If this property contains invalid headers, HTTP requests may fail.
This property is useful for fine-tuning the functionality of the provider to integrate with specialized or nonstandard APIs.