For accessing exchange 365, there is a whole list of IPs that needs to be bypassed via firewall:
But still microsoft maintains that the IPs are dynamic and subject to change and we need to subscribe to an RSS feed to keep track of these IP changes.
Is there an easier way out to let our Firewall / proxy access office 365 un-hindred? microsoft suggests to configure firewall rules based on DNS rather than IP but Cisco's ASA series doesn't support that.
Also, any other security precautions we need to consider while opening up these access IPs/ ports to microsoft DCs?