Microsoft 365 uses 34 prefixes for Exchange Online.
Short answer
Exchange Online: mail, calendar and Outlook connections.
Prefixes
What changed
No prefixes added or removed since we started tracking this list. Changes appear here the day after the provider publishes them.
Allowlist formats
nginx (first 5 prefixes)
allow 104.47.0.0/17; allow 13.107.128.0/22; allow 13.107.18.10/31; allow 13.107.6.152/31; allow 131.253.33.215/32; deny all;
iptables (first 5 prefixes)
iptables -A INPUT -s 104.47.0.0/17 -j ACCEPT iptables -A INPUT -s 13.107.128.0/22 -j ACCEPT iptables -A INPUT -s 13.107.18.10/31 -j ACCEPT iptables -A INPUT -s 13.107.6.152/31 -j ACCEPT iptables -A INPUT -s 131.253.33.215/32 -j ACCEPT
Generate the full list from the CSV, and refresh it on a schedule: providers add and retire prefixes often.
Sources
- Microsoft 365: published IP ranges · checked 6 Nov 2026
- Microsoft 365 documentation