If you come across the issue of saving the IP which needs to block it under the “Edge server IP Block List” entry, following error receive “The server threw an exception. (Exception from HRESULT: 80010105 (RPC_E_SERVERFAULT))”

Why this is used : IP Block List is part of the connection filtering feature in Exchange. When the IP Block List feature is enabled on a computer, the Connection Filter agent analyzes all messages that come through all Receive connectors on that computer and it block all incoming messages from addresses specified in the IP Block list.

Reason for the above error : Duplicate IP exist inside the IP block list.

Resolution : From the EMS (Exchange management shell) use the following. You use the Add-IPBlockListEntry and Remove-IPBlockListEntry cmdlets to manage the addresses in the IP Block list. You can specify individual IP addresses, IP subnets using the CIDR notation, or IP ranges.

From the EMS,

If you want to list all the IP blocklist for verification, type  Get-IPBlockListEntry . This will list all the Block IP, and you can see the duplicate entries. Write down each of the dupicate entry seperately and then run the following command for each entries.

To remove an address from the IP Block list using the Shell, you must specify this IP. However, an easier way to remove an address is to pipeline the output of the Get-IPBlockListEntry cmdlet to the Remove-IPBlockListEntry cmdlet.

For example, if you want to remove the IP address 192.168.1.100 from your IP Block list, run the following command:

Get-IPBlockListEntry -IPAddress 192.168.1.100 | Remove-IPBlockListEntry

This will remove 192.168.1.100 from your IP block list, which is a duplicate, identified by you. For each entry, do the same by changing the IP. Once it is done, Your block list will start accepting the IP to block and  save it on the list, without throwing the error (as above mentioned)