Hi,
We have been an Office 365 customer for the last 2 years, as a gold partner, on an E3 trial plan with 250 user licenses. Our trial ended in May this year and we have been dropped down to using only our partner allowance of 100 user licenses, which we are nearly at the limit of. So I wanted to start using our on premises mailserver for service mailboxes and O365 for all users mailboxes, we have a number of mailboxes that are used for our helpdesk software and some other internal mail services.
We are running ADFS with SSO with load balanced federation servers and proxy servers, but I really wanted to know the best way to achieve my goal. My initial thought was to add an MX record, with a lower priority than the O365 MX record, that points to our On prem exchange to pick up any mail destined for mail addresses not on O365, but this...