The autodiscover CNAME record enables autodiscover for Outlook clients. Users can then simply enter their email address into Outlook to set up OutlookAnywhere access, based on that user’s domain suffix.
With a cloud-only configuration, the MX record routes incoming mail to ExchangeOnline through the ExchangeOnline Protection service. This service is available as a stand-alone offering, in which case the MX records will point to the cloud service.
The SPF (TXT) record provides the Sender Policy Framework anti-spam protection. SPF records ensure that destination email servers trust the messages sent from your domain in Office365. The SPF record makes all messages from your domain appear to originate from the Office 365 messaging server