On TechNet we publish the range of IP addresses that are used when sending mail out of a custom EOP connector. If you have created an EOP on-premises connector to deliver inbound mail to your on-premises mail environment, or an EOP partner connector to deliver mail to a partner, the IPs used in these situations are the ones we publish. These published ranges DO NOT include the IPs that are used to deliver mail that does not leave through a custom EOP connector.
Effective as of January 1, 2015, additional IP ranges have been added to support the growth of the service. For organizations that lock down their on-premises mail environment to only accept mail from EOP, you will need to allow these additional IP ranges. This also applies for organizations that accept mail from you through a custom EOP outbound connector, if they lockdown their inbound mail from you to the published EOP IP ranges.
As we have noted on the TechNet page, organizations that started using EOP prior to January 1, 2015, do not need to take immediate action, but we recommend that you add these new IP ranges to your environment as soon as you can.
As of today, January 6, 2015, the range of IPs used by custom EOP connectors are as follows.
Current EOP IP ranges for custom connectors can be found at the links below.