Large-Scale Mail with Postfix, OpenLDAP and Courier

Now that slapd is configured, it's time to start adding data to the LDAP directory. We use the command-line tools that come with OpenLDAP and create LDIF files to modify the directory.

The first step is to create a base tree structure with our root node, the hosting organization and an entry for the rootdn. Create a file called base.ldif with the following contents:

dn: dc=myhosting, dc=example
 objectClass: top
 dn: cn=Manager, dc=myhosting, dc=example
 objectClass: top
 objectClass: organizationalRole
 cn: Manager
 dn: o=hosting, dc=myhosting, dc=example
 objectClass: top
 objectClass: organization
 o: hosting

Now use ldapadd, binding as the root account, to add this LDIF:

ldapadd -x -D "cn=Manager,dc=myhosting,dc=example" \
-w secret -f base.ldif

Domains can now be added under the hosting tree. Each domain needs to have postmaster and abuse entries at minimum. To make a tree for domain1.example, create a file called domain1.example.ldif with the following contents:

dn: o=domain1.example, o=hosting, dc=myhosting,
 dc=example
objectClass: top
objectClass: organization
o: domain1.example
dn: cn=postmaster, o=domain1.example, o=hosting,
 dc=myhosting, dc=example
objectClass: top
objectClass: organizationalRole
objectClass: CourierMailAlias
cn: postmaster
mail:
maildrop: postmaster
dn: mail=abuse@domain1.example, o=domain1.example,
 o=hosting, dc=myhosting, dc=example
objectClass: top
objectClass: CourierMailAlias
mail:
maildrop: abuse

Notice that the maildrop attributes are local e-mail accounts and will forward to the postmaster and abuse accounts in /etc/aliases. There are no accounts in the postmaster role, so only the root account can create accounts at the moment. Add this domain with the following command:

ldapadd -x -D "cn=Manager,dc=myhosting,dc=example"
\
-w secret  -f domain1.example.ldif

Now, let's add an account with an e-mail <user1@domain1.example>. Let's also grant this account postmaster privileges for domain1.example. Create a user1.domain1.example.ldif with the following contents:

dn: mail=user1@domain1.example, o=domain1.example,
 o=hosting, dc=myhosting, dc=example
objectClass: top
objectClass: CourierMailAccount
mail:
homeDirectory: /home/vmail/domains
uidNumber: 101
gidNumber: 101
mailbox: domain1.example/user1
dn: cn=postmaster, o=domain1.example, o=hosting,
dc=myhosting, dc=example
changetype: modify
add: roleOccupant
roleOccupant: mail=user1@domain1.example,
 o=domain1.example, o=hosting,
 dc=myhosting, dc=example

The first section adds a new entry for the account. The home directory and mailbox point to the physical mailbox on the filesystem. The uidNumber and gidNumber attributes are required but not used, so they are filled in with dummy values of 101. The second section modifies the postmaster entry by adding a roleOccupant attribute with the DN of user1@domain1.example. Let's create this account:

ldapadd -x -D "cn=Manager,dc=myhosting,dc=example"
\
-w secret -f user1.domain1.example.ldif

ldappasswd -x -D "$DN" -w $PW -s user1 \
"mail=user1@domain1.example, o=domain1.example,
o=hosting, dc=myhosting, dc=example"

We cover only the sections of Postfix that pertain to the mail hosting. To deal with other parts of Postfix setup, please visit the Postfix web page.

Download the Postfix source and untar it. You need to rebuild the Postfix Makefiles to be aware of LDAP and link against it. To do this, execute the following command:

make makefiles CCARGS="-I/usr/local/include
-DHAS_LDAP" AUXLIBS="-L/usr/local/lib -lldap
-L/usr/local/lib -llber"

At this point, follow the normal Postfix compiling and installing instructions as documented in its INSTALL and LDAP_README files.

While configuring Postfix for this task, we are mostly concerned with /etc/postfix/main.cf. For most of the Postfix configuration, you will configure in a way that makes the most sense for your site, and you can follow the documentation contained in the Postfix source or on the Postfix web site. Here, we talk about the settings that are affected by this setup. If any of the configuration examples shown below aren't explicitly attributed to a specific file, assume they can be found in main.cf.

The transport table maps domains to message delivery transports (as specified in /etc/postfix/master.cf) and/or relay hosts. For our virtual domains, we want to map them to the virtual delivery agent that comes with Postfix. A transport table could look something like this:

domain1.example           virtual:
domain2.example           virtual:

After making your transport table in plain text, you need to make it into a binary DB file using postmap (see man postmap). At this point, tell Postfix that there is a transport table and where to find it. You also need to let Postfix know that we accept mail for those domains. This is done through the transport_maps and mydestination directives:

transport_maps = hash:/etc/postfix/transport
mydestination = $myhostname, localhost.$mydomain,
  $mydomain, $transport_maps