HOTSPOT
A company plans to deploy an Office 365 tenant.
You have the following requirements:
Administrators must be able to access the Office 365 admin center.
Microsoft Exchange Online must be used as a Simple Mail Transfer Protocol (SMTP) relay for a lineof-business application that sends email messages to remote domains.
All users must be able to use the audio and video capabilities in Microsoft Lync 2013.
You need to configure the ports for the firewall.
Which port should you use for each application? Select the correct answer from each list in the
answer area.
Answer: 
Explanation:
SMTP Relay should be 587: http://blog.hametbenoit.info/Lists/Posts/Post.aspx?ID=249
Read RFC 6409
When conforming to this document, message submission uses the protocol specified here, normally over port 587.
Message relay is unaffected, and continues to use SMTP over port 25.
I agree with ArneT.
MoreOver,
the question is about SMTP relay for an application (not lync… which could be confusing with 587)
Visit this website and you can find the right answer which is port 25.
https://technet.microsoft.com/en-us/library/dn554323(v=exchg.150).aspx#option3
How to set up a multifunction device or application to send email using Office 365
Open network port – SMTP relay – 25
Its 587 (recommended) or 25
seeing as Microsoft thinks their are the center of the universe on the test I would go with 587
https://support.office.com/en-us/article/How-to-set-up-a-multifunction-device-or-application-to-send-email-using-Office-365-69f58e99-c550-4274-ad18-c805d654b4c4