HOTSPOT
You are the Exchange Online administrator for an organization. The organization migrates all users
to Exchange Online. An employee works for a partner organization named Contoso, Ltd. The
employee uses the email alias employeel©contoso.com.
Users report that over the past week, they have not received email messages from
[email protected].
You need to trace email messages that originate from [email protected] to users inside your
organization.
In the message trace window, which two settings should you configure? To answer, select the
appropriate objects in the answer area.
Answer: 
Explanation:
Sender and Last 48 hours… Is the right selection
I would say recipient and last 48 hours because the sender is not a member of your tenant and you can only select users that have a mailbox or are know as contact in your tenant
Then to agree with Damigs:
It says that you need to trace from the originator. And it is not prudent to search from every single recipient. You want to search if you are getting the email in your domain.Ideally getting a link to justify our answers would be better.
Jo – you can manually type in “employeel©contoso.com” in the Check Names field.
BC is correct. I connected to our office 365 Message Trace.
“Select a user from the list and click Add. To add recipients who aren’t on the list, type their email addresses and click Check names.”
I was able to trace emails from another organization.
So the Sender is correct.
but why 48 hours ?
You would want to change from 48h to one week, so that is why you would select 48h
sender and time