Hi Perry,
As users of Plan p, Office365 suggest you point your domain’s Name Server to Office365. Office 365 will automatically create all the DNS records that are required for the domain name to work with each service.
Of course, you also can use your domain name with Office 365 without redirecting your Name Server records to Office 365. But there will be limitations on your Office 365 services, more information, see this link: http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/hh416759.aspx#bkmk_limits .
To add your domain to Office 365 but continue to manage your domain's DNS records, please point your domain’s Name Server to Office365 to finish all verifications at first, then you can re-point the Name Server back to previous addresses.
After you finished these , Do not forget to create corresponding records for Office365 at your domain registrar: http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/jj655390.aspx
Thanks,
Jacky Ding