HOTSPOT
You are the Office 365 administrator for Contoso, Ltd.
An employee with the user name User1 has requested a secondary email address of
[email protected].
You need to assign the secondary email address.
How should you complete the relevant Windows PowerShell script? To answer, select the
appropriate option from each list in the answer area.
Answer: 
Explanation:
Whilst this will do the trick it will knock out the sip address and the new SPO addresses they seem to have appeared out of nowhere example
SPO:SPO_ef6bdb7a-c624-4cda-95dd-b8b67c2da20b@SPO_13bb99a0-e1da-4017-afcf-51ae561264f1
https://community.office365.com/en-us/f/148/p/440165/1125651#1125651
I used a measure up test and they were asking a similar question but using the -add feature to leave the existing emailaddresses untouched. You can see something similar here under 1.4 Set Alias Email address (Method 1)
Read more http://o365info.com/manage-email-address-using-powershell/
http://o365info.com/manage-email-address-using-powershell/
Valid syntax for email address parameter is []:,[]:….
SMTP The primary SMTP address. You can use this value only once in a command.
smtp Other SMTP email addresses.
X400 X.400 addresses in on-premises Exchange.
X500 X.500 addresses in on-premises Exchange.
If you don’t include a value for an email address, the value smtp is assumed.
——-
Set-Mailbox -SecondaryAddress
The SecondaryAddress parameter specifies the secondary address used by the UM-enabled user.
or use -emailaddresse @{add=”[email protected]”} to add the email to all others currently used.
This is the only working answer, but it will remove all other email addresses the user could have, including SIP, @domain.onmicrosoft.com and possible post-migration X500 ones. That would be BAD.
answer is corect