Linux tips and tricks

Part 7. Alternative methods for storing user settings. Using Windows AD.

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Category: Mail Server

Published: Friday, 21 June 2019 16:12

Written by Super User

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In large organizations, mail servers and other services are often integrated with the Windows AD

Assume that we have Windows domain named the study.local and there is a special user mailadmin with the password mailadmin. And he has permissions to read from the LDAP tree. The domain controller has the address 192.168.0.10. Domain users must have aт attribute “mail” filled in. It should contain the mailing address of the user. Domain groups are created to work with mail aliases. They also fill in the attribute “mail”. Letters that arrive to such groups must be forwarded to all users who are their members.  

Postfix configuring

First we will install LDAP support in Postfix

# apt install postfix-ldap

We will add support for the data in the LDAP database to the /etc/postfix/main.cf file

virtual_alias_maps = hash:/etc/postfix/virtual mysql:/etc/postfix/aliase.cf ldap:/etc/postfix/ldapalias

virtual_mailbox_maps = hash:/etc/postfix/vmailbox mysql:/etc/postfix/box-sql.cf ldap:/etc/postfix/ldap_virtual_mailbox_maps.cf

Again, we do not disable previous settings, but add new data sources.

Next, you need to create LDAP query files.

To process the user's mailing addresses, we will create a file /etc/postfix/ldap_virtual_mailbox_maps.cf and write to it

server_host = 192.168.0.10

bind = yes

bind_dn = cn=mailadmin,cn=Users,dc=study,dc=local

bind_pw = mailadmin

search_base = cn=Users,dc=study,dc=local

query_filter = (&(mail=%s))

result_attribute = mail

result_format = %d/%u/

To process mail aliases, we will create a file /etc/postfix/ldapalias and write to it

server_host = 192.168.0.10

bind = yes

bind_dn = cn=mailadmin,cn=Users,dc=study,dc=local

bind_pw = mailadmin

search_base = cn=Users,dc=study,dc=local

query_filter = (&(objectClass=group)(mail=%s))

leaf_result_attribute = mail

special_result_attribute = member

Now Postfix can receive mail by reading data from the AD.

Dovecot configuring

First, we will install LDAP support in Dovecot

# apt install dovecot-ldap

Uncomment string in the file /etc/dovecot/conf.d/10-auth.conf

!include auth-ldap.conf.ext

And again, we do not disable old data sources, but just add a new one.

In the /etc/dovecot/dovecot-ldap.conf.ext file, we will provide information about connecting to the domain controller and queries.

hosts = 192.168.0.10

auth_bind = yes

ldap_version = 3

base = cn=Users,dc=study,dc=local

dn = cn=mailadmin,cn=Users,dc=study,dc=local

dnpass = mailadmin

deref = never

scope = subtree

user_filter = (&(ObjectClass=person)(sAMAccountName=%u))

pass_filter = (&(ObjectClass=person)(sAMAccountName=%u))

Note that passwords are stored in LDAP as a hash. Due to the fact that the hashing is not an inverse operation, it's impossible to convert a hash from one type to another. That is why we used PLAINTEXT authentication when setting up the mail server. To securely transfer logins and passwords, you must use encrypted client connections with the mail server.

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