We have a fresh installation Exchange Server 2016. The issue is when I send emails to outlook it goes to junk folder only for outlook, for other email service providers it properly reach inbox. I have checked the ip and not blacklisted on any RBLs and also added SPF records. But we are not using the on-premise exchange server as our primary email service so the MX record is pointed to Rackspace server, but I added the exchange server on MX record with low priority. I have added the email header and also added the spf record. I am not able to understand email header properly, please suggest a solution
"v=spf1 mx ptr ip4:66.***** a:exchange.******.com ?all"