The correct answer is D. When delivering mail to example.com the protection server tries to connect to the Destination MTAs starting at the top one and working down the list .
The exhibit shows that the inbound mail route for example.com is configured with three destination hosts:
m1.example.com
m2.example.com
m3.example.com
It also shows that the Delivery Type is set to Ordered . In Proofpoint route configuration, Ordered means the system uses the listed destinations in sequence, following the order in which they appear in the route. That means the first connection attempt is made to the top entry , then if needed it proceeds downward through the remaining hosts.
Why the other choices are incorrect:
A is incorrect because ordered delivery does not start from the bottom of the list.
B is incorrect because multiple destination hostnames can be listed in an ordered route; they do not have to be IP addresses only.
C is incorrect because there is no requirement shown here for a minimum of five MTAs for ordered delivery.
This is a Mail Flow question focused on route behavior. The main concept being tested is how Proofpoint uses the destination list when Ordered delivery is selected. The configured order matters, and the Protection Server follows that order from top to bottom .
So the complete interpretation of the exhibit is that the Protection Server attempts delivery starting with m1.example.com , then m2.example.com , then m3.example.com , which makes Answer D the verified course-aligned choice.