When you're setting up DNS records to route email for your domain, it's important that you have or create only one TXT record for SPF. If you already have an SPF record, you should append the new Office 365 values to it, rather than create a new one.
After you've added or updated your SPF record for Office 365 email, you should check to make sure that the syntax is correct. This helps avoid email delivery and spam classification issues. Office 365 does not provide a way to test your SPF record, but a number of tools are available that can help you, including the following: