[Chapter 16] 16.6 Things to Try
Author: Bryan Costales & Eric Allman
Date: 1999-01-06T18:39:49Z

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| Chapter 16 The null.mc File and m4 |

## 16.6 Things to Try

- Take a little time to contrast the client.cf file created in the prior 11 chapters with the one created in this chapter. How and why do they differ? You may have to leap ahead to the reference chapters.

- The cf/README file suggests that the FEATURE(`nocanonify`) can be used with null.mc. What pitfalls do you foresee with the use of this feature?

- Neither version of client.cf uses any aliasing or forwarding. Consequently, neither will ever have to send addresses such as programs or files to the hub:

  >     |/run/this/program         a program
  >     /put/in/this/file          a file

  What happens if you try to send one by hand? Why is it necessary for a client.cf file to avoid delivering these kinds of addresses itself?

- In the original client.cf file we forwarded the mail to the hub's alias mailhost. What would happen if we used that name in the nullclient feature?

  >     FEATURE(`nullclient',`mailhost')

- Suppose you want to tune the rules in the m4(1) produced client.cf file? Does cf/README tell you how? Does the `nullclient` delivery agent have `S=` or `R=` that you can use?

16.5 Qualify All Addresses? |  | 17. The Hub's Complex Rules