Zendesk maintains this list of public IP addresses to allow customers to provide whitelist rules for access to their internal resources by Zendesk servers.
LAST UPDATED: December 6, 2013 (added: 188.8.131.52/24 range)
Note: This list should be considered exhaustive and complete as of the date listed above. There may, from time-to-time, be new IP addresses added or removed. We will strive to provide advanced notice of these changes, though it may be operationally necessary to add new IP addresses on an emergency basis on rare occasions.
Outbound Email Servers are listed in our spf record, which we update as needed. Our spf record can be read by these commands: