Error: stopped working (IPs on the Blocklist and RBLs were no longer being blocked).
This blog post clarifies the confusion about "when" connection filtering is applied and how configuration settings are applied when the agents are installed on a Hub server.
Let's begin by looking at the online documentation regarding Connection Filtering:
“By default, connection filtering is enabled on the Edge Transport server for inbound messages that come from the Internet but are not authenticated. These messages are handled as external messages. You can disable the filter in individual computer configurations by using the Exchange Management Console or the Exchange Management Shell.
When connection filtering is enabled on a computer, the Connection Filter agent filters all messages that come through all Receive connectors on that computer. As noted earlier in this topic, only messages that come from external sources are filtered. External sources are defined as non-authenticated sources. These are considered anonymous Internet sources.”