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Chapter 15. Email

15.3.6. Using Sendmail with LDAP

Using the 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 the following:

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/mail/sendmail.cf

file by running

m4

and restarting Sendmail. See Sec 

tion 15.3.4 for instructions on doing this.

For more information on LDAP, see Chapter 18.

15.4. Fetchmail

Fetchmail is a program that can retrieve email from remote servers for on demand TCP/IP connec 

tions. Many users appreciate the ability to separate the process of downloading their messages located

on a remote server from the process of reading and organizing their email in an MUA. Designed with

the needs of dial up users in mind, Fetchmail will connect and quickly download all of your email

messages to your mail spool file using any number of protocols, including the POP3 and IMAP. It can

even forward your email messages to an SMTP server, if necessary.

Before attempting to use Fetchmail, be sure that it is installed on your system. If it is not, you can

install it using the

fetchmail

RPM on the Red Hat Linux CD ROMs.

Fetchmail is configured for each user through the use of a

.fetchmailrc

file in the user's home

directory. A program bundled with Fetchmail, called

fetchmailconf

, is very helpful for configuring

a basic

.fetchmailrc

file that you can customize at will.

Using preferences in the

.fetchmailrc

file, Fetchmail will check for email on a remote server and

pull it off, attempting to deliver it to port 25 on the local machine, using the local MTA to place the

email in the correct user's spool file. If Procmail is available, it can then be used to filter the email and

place it in a mailbox so that it can be read by an MUA.