Unable to create a connector ' contains reserved IP addresses.

Hello Gambit C.

Good day. Thank you for posting in the community!

Sincere apologies for any inconvenience this issue might be causing you.

Based on your provided information, it seems the issue you are facing is related to using a reserved IP address range for your SMTP relay configuration in Exchange Online.

To resolve this, you will need to ensure that the IP address or IP address range you are using for the SMTP relay is not a reserved IP range. 

Reserved IP address ranges are typically not allowed for SMTP relay configurations in Exchange Online, as the service requires a static IP address or address range that is not part of a reserved network. 

You can try using a different, non-reserved IP address or IP address range for your SMTP relay configuration. Alternatively, you can check the logs on the Proofpoint side to see the specific source IP address that is being rejected and why it is considered a reserved IP range.

Additionally, ensure that you have properly configured the inbound connector in your Exchange Online organization, as the error message suggests there may be an issue with creating or updating the inbound connector. 

For further investigation, it is recommended to raise a support ticket to Microsoft Technical Support Team. The engineers in the related team have higher permission and resources than us to help collect logs and check the root cause directly. you contact your Microsoft 365 administrator and follow the steps in this article https://learn.microsoft.com/en-us/microsoft-365/admin/get-help-support?view=o365-worldwide&tabs=online#online-support to create a support ticket to Microsoft.

You can also call MS support via- https://support.microsoft.com/en-us/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2

Sincerely,

Md Ashabul Haque | Microsoft Community Moderator