If you want to set up email using a 2nd domain or sub domain (Enterprise accounts only), you may have a tough time finding instructions from MSFT. And if they exist at all, MSFT’s instructions are often questionable when it comes to dns management. The key is using the correct dns records.The example sub domain I’m using here is: 365.domain.com.
Add the domain/sub domain to your account (sub domains of already verified domains don’t need to be verified).
Domain intent can be Exchange /Lync OR Sharepoint if you want to use the domain with a public web site (it doesn’t really matter!)
Log into your registrar’s dns zone editor and add the following records (replace “365” with the “sub” part of your sub domain):
v=spf1 include:spf.protection.outlook.com –all
As mentioned above, as long as the records are correct, it doesn’t seem to matter what you set “domain intent” as. So if you want to use this domain with a public site too, just choose “Sharepoint” and your Exchange email will still work fine.
To see how to set that up, look for “Use separate sub domains (or domains) for BOTH your 365 public sites! ” in this blog.