Configuring a Mail Server

About this document
Change the Cw setting
Remove the hostname in the "from line"
Refresh sendmail.cf file
Create aliases

About this document

The information in this document describes the procedure for configuring your mail server and applies to AIX Versions 4.2.x and 4.3.x. Root authority is required for this process.

NOTE: The following configuration steps do not implement the open relay control features available in sendmail 8.8.8 and 8.9.3, which allows you to block spam attacks. For implementation of open relay control features (anti-spamming or anti-relaying), please refer to the following documents: Configuring Anti-Spam in AIX 4.3.2 and Configuring Anti-Spam in AIX 4.3.3. This configuration is recommended for mail servers that are potentially vulnerable to open relay attacks.

Change the Cw setting

You must tell sendmail to accept mail addressed to <user>@test.com. This is accomplished by changing the setting of the Cw macro in the sendmail.cf file.

Using your preferred editor, open the sendmail.cf file:
```
           /etc/sendmail.cf
```

Find the following entries:

          #Cw localhost $w $?m$w.$m$. YourHostAliases
          #Cm $m YourOtherDomainNames
          Cwlocalhost

Change to the following:

          Cw localhost $w $?m$w.$m$. test.com
          #Cm $m YourOtherDomainNames
          #Cwlocalhost

Remove the system's hostname in the "from line"

Now tell sendmail to remove the system's hostname in the from line. This is necessary to allow recipients to reply to messages sent out. Assume that the relay machine's full name is relay.test.com.

By default, any mail sent out from this relay will be from the following:

          <user>@relay.test.com

The conventional method will have the from line display the message below:

          <user>@test.com

You will need to make two changes to the sendmail.cf file for configuration.

Set the DM macro:

The original setting follows:

          # who I masquerade as (null for no masquerading) (see also $=M) DM

Change this setting to the following:

          DMtest.com

Modify a ruleset:

Original setting:


###################################################################

###  Ruleset 94 -- convert envelope names to masqueraded form   ###

###################################################################
S94
R$* < @ *LOCAL* > $*    $: $1 < @ $j . > $2
#R$+                    $@ $>93 $1          <-

[This last line may not be listed.]----------- 
Change this to:
###################################################################

###  Ruleset 94 -- convert envelope names to masqueraded form   ###

###################################################################
S94
R$+                    $@ $>93 $1

Save the /etc/sendmail.cf file.

Refresh the sendmail.cf file

Enter the following command:

          refresh -s sendmail

This updates sendmail with the new configurations. If sendmail is not running, you need to check to see if it is active using the following command:

          lssrc -s sendmail

Information similar to the following will be displayed.

          Subsystem         Group            PID     Status 
          sendmail          mail             5424    active

If it is not active, start it up by issuing the following command:

          startsrc -s sendmail -a "-bd -q30m"

Create aliases

sendmail must be told where to send mail it receives for users that do not exist on the relay machine. This is done using the /etc/aliases file. For example, if a user has a username of John on machine nixon.test.com, we must add the following entry to this alias file:

john:john@nixon.test.com

NOTE: If you want a specific message to be delivered to more than one user, just add another alias separated by a comma and a space.

For example:

          john:john@nixon.test.com, frank@venus.test.com

After saving the aliases file, you need to run:

          newaliases

This rebuilds the alias database. Now, when mail is sent to john@test.com, it will be relayed to john@nixon.test.com.

NOTE: Other machines within the network should also revise their from lines to exclude the hostname. This is done by repeating step two on each host, followed by a refresh of the sendmail daemon. This is called masquerading and is necessary so that mail from john@nixon.test.com goes out as john@test.com. This will allow john to receive message replies.