Why would you consider sending an email to an address that you know does not exist within the company you are performing a Penetration Test for?

Why would you consider sending an email to an address that you know does not exist within the company you are performing a Penetration Test for?
A . To determine who is the holder of the root account
B. To perform a DoS
C. To create needless SPAM
D. To illicit a response back that will reveal information about email servers and how they treat undeliverable mail
E. To test for virus protection

Answer: D