Details
By default, sender filtering is enabled on a computer performing the Edge Transport server role for inbound messages from the Internet that are not authenticated. These messages are handled as external messages. You can disable the Sender Filter agent in individual computer configurations by using the Exchange admin center or the Exchange Management Shell. When you enable the Sender Filter agent on a computer running Exchange, it filters all messages from all Receive connectors on that computer. Only messages from external sources are filtered. External sources are defined as non-authenticated sources. These are considered anonymous Internet sources.
Rationale:
Spam consumes a large amount of network bandwidth and server capacity. In addition, it is often the source of malicious software.
Solution
To implement the recommended state, execute the following PowerShell cmdlet:
Set-SenderFilterConfig -Enabled $true
Supportive Information
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: System and Information Integrity.This control applies to the following type of system Windows.