Use warnings to MTA option

Notification message MTA options:  (0 or 1)
DELETED. With the advent of standardized notification handling, this option was deprecated and is now deleted.

The  MTA option controls whether or not the MTA makes use of the information contained in Warnings-to: header lines when returning messages. Setting this option to 1 directs the MTA to make use of these header lines. The default is 0, which disables use of this header line. Note that this default represents a changes from the default in early versions of PMDF.

See also:
 * Notification message MTA options