Instructs the task to include or ignore message headers.
If IncludeHeaders is set to True, the task will include any headers retrieved from the server in the message. This is useful for PassThrough configurations and for orchestrations that use MIME decoding message pipelines.
Note: regardless of the value of this property, there will be a "MessageHeaders" field of MessageList that contains a string with the full RFC-822 encoded original headers as retrieved from the server. This is useful for situations where it is necessary to find specific mail headers.
This property is not available in the Sender.