I do not have an instance to test, but you can create an O365 list in minemeld:
In the past I have used the API and a powershell script to pull the list from Microsoft and create a dynamic address list from that, here are a few articles to point you in the right general direction:
A smiliar strategy could be used to dump the list to an EDL if you have somewhere available to host it.
I thought I'd comment for anyone reading this who doesn't have the systems to implement Mindmeld, and is looking for an on-prem Windows solution.
Microsoft has a powershell method of getting the latest o365 IP Addresses into a text file. You can then host that file on an IIS server, script Powershell to keep it up to date and point a PAN EBL at this file. Works great. One catch, the Microsoft Powershell script puts CR-LF at the end of each line and apparently EBL can only handle LF. So you'll need to edit the powershell script and add this line after the out-file statement: (Get-Content $datapath -Raw).Replace("`r`n","`n") | Set-Content $datapath -Force
That will replace the CRLF with just LF.
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