A company plans to use Office 365 to provide email services for users.
You need to ensure that a custom domain name is used.
What should you do first?

A.
Add the custom domain name to Office 365 and then verify it.

B.
Verify the existing domain name.

C.
Create an MX record in DNS.

D.
Create a CNAME record in DNS.

Explanation:
A: DNS actually tells the Internet where to send email to. Thus you need to make sure that your custom name
that you intend using for email is added to Office 365 and verified. When you put the right information into the
right DNS records for your domain, the DNS system routes everything correctly so your email, for example,
arrives in Office 365 instead of somewhere else.