Office 365 network IP Addresses and URLs are no longer available in XML format.
You should transition to accessing the data in JSON format as described at http://aka.ms/ipurlblog.
This was first announced on 2 April 2018 and the XML file was last updated on 22 September 2018.
Microsoft publishes its IP address listings for various services here:
https://support.content.office.net/en-us/static/O365IPAddresses.xml
Using this list, I can generate iptables firewall rules to only allow incoming SMTP traffic from Microsoft, and hopefully keep my ruleset updated automatically when they change things.
I'm using the XPath support in xml.etree.ElementTree, and I experimented until I got what I wanted, so it's possible there's a better way.
I wrote this (badly?) in Python because hey, who doesn't want to learn how to mangle XML in another language?