issues with sending and receiving email

was working before I decided to use Office 365 for email but have since decided I did not need office or the exchange server so I let it go trying to get my cpanel email to work now and cannot get it working after reconfiguring DNS to point to my cpanel email it is giving me + 550 The mail server could not deliver mail to xxxx@domain.us. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.