What is the most likely reason why the message fails to appear in the message trace?

You have a Microsoft Exchange Online tenant that contains 1,000 users.

A user recently sent an email message that was never received by a recipient on the internet. From the Exchange admin center, you successfully run a message trace but cannot see the message in the trace.

What is the most likely reason why the message fails to appear in the message trace?
A . The user addressed the message to multiple internal and external receipts
B . The user encrypted the email message.
C . Your administrative user account requires additional rights.
D . The message is in the user’s Outbox folder.

Answer: D