SPF (Sender Policy Framework) is used by Office 365 to filter incoming messages. And once you are using Office 365 you already have included something like spf.protection.outlook.com to your domain records. The record confirms that Microsoft can send messages on your behalf.
"v=spf1 mx include:spf.protection.outlook.com include:spfrerouting.xink.io ~all"
Please note that spfrerouting.xink.io includes a soft fail option, if it is not acceptable in your case, just add our IP addresses directly. 52.186.121.110 for US data center and 40.68.36.243 for EU data center.
"v=spf1 mx include:spf.protection.outlook.com ip4:52.186.121.110 -all"