Today I had the issue ( after some years again ) that I could not see the rules tab inside the configuration document for a specific mail server:

I did the mentioned steps in the following IBM TN:

Create a Formula agent, designed to act on selected documents, to delete the field ActForm:
Steps to create the agent:
1. Start the Domino Designer client and open the Domino Directory database.
2. From the menu, select Create -> Agent.
3. The Agent Properties dialog will appear. Give the agent a name. The Runtime settings can be left at the defaults of “Action Menu Selection” and “All Selected Documents”.
4. Click on the X mark in the upper righthand corner to close and save the Agent Properties settings. 5. In the main pane, change the “Run” keyword selection from “Simple Action(s)” to “Formula”.
6. Enter the following code into the main window: FIELD ActForm :=@Deletefield
7. From the menu select File -> Save.
8. Exit from the Domino Designer client.

Steps to run the agent:
1. Open the Domino Directory from the Notes client.
2. Open the view Configuration -> Servers -> Configurations.
3. Select the affected configuration documents.
4. From the menu select Actions -> <agent name>.

Now when the Configuration document is opened from the Notes client, the Rules tab will display as expected.