Using Sendmail with LDAP

As we have already seen in Chapter 4, Lightweight Directory Access Protocol (LDAP) is a very quick and powerful way to find specific information about a particular user from a much larger group. For example, you could use an LDAP server to look up a particular email address from a common corporate directory by a user's last name. In this kind of implementation, LDAP is largely separate from Sendmail, with LDAP storing the hierarchical user information and Sendmail only being given the result of LDAP queries in pre-addressed email messages.

However, Sendmail supports a much greater integration with LDAP, where it uses LDAP to replace separately maintained files, such as aliases and virtusertables, on different mail servers that work together to support a medium- to enterprise-level organization. In short, you can use LDAP to abstract the mail routing level from Sendmail and its separate configuration files to a powerful LDAP cluster that is being leveraged by many different applications.

The current version of Sendmail contains support for LDAP. To extend your Sendmail server using LDAP, first get an LDAP server, such as OpenLDAP, running and properly configured. Then, you need to edit your /etc/mail/sendmail.mc to include:

LDAPROUTE_DOMAIN('yourdomain.com')dnl
FEATURE('ldap_routing')dnl

	Note
	This is only for a very basic configuration of Sendmail with LDAP. Your configuration should differ greatly from this depending on your implementation of LDAP, especially if you wish to configure several Sendmail machines to use a common LDAP server. Consult /usr/share/doc/sendmail/README.cf for detailed LDAP routing configuration instructions and examples.

Next, recreate your /etc/sendmail.cf file by running m4 and restarting Sendmail. See the section called Common Configuration Changes for instructions on doing this.

For more information on LDAP, see Chapter 4.