History to return MTA option

Notification message MTA options:  (1-200)
The  MTA option controls exactly  how many delivery attempt history records are included in returned messages, when   is set to enable such inclusion. The delivery history provides some indication of how many delivery attempts were made and in some cases indicates the reason the delivery attempts failed. The default value for this option is 20.

See also:
 * Notification message MTA options
 * Notification message format
 * return_delivery_history MTA Option