o365 NAT Rules for MX100

[Azimuth1]

I have inherited an existing MX100 firewall and it has a NAT rule for o365/Exchange/Hybrid.

Since a public IP is assigned for use with o365 email, I am thinking there is a better way to restrict inbound Microsoft traffic.  Currently inbound traffic from ANY is allowed.  I would like to tighten inbound email traffic without breaking something.  Has anyone else done this with an MX?

[PhilipDAth]

It's a real pain in the neck.

You need to load in all the IP address ranges:

https://docs.microsoft.com/en-us/office365/enterprise/urls-and-ip-address-ranges 

And the ranges change from time to time, so you need to keep checking back and updating them.

[Aaron_Wilson]

So Microsoft a few months ago started advertising how they had just a couple summaries that covered their entire suite of O365, etc. It was a fairly large range, but I was calling Bullock's on it since there was little documentation on it and their articles with the smaller summaries were not updated.

Now I can't find anything on those small summaries, so maybe they retracted it.