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my system is set up like this.

smtp --> postfix --> dovecot (via LMTP) --> mailbox

The tricky part is that authentication is against LDAP.

A typical LDAP entry looks like this:

CN=Jon Doe
uid=jond
mail=jonny@example.com

What now happens is that postfix is pushing the mail to dovecot. Dovecot is performing an userdb lookup but based on the destination email address that is "jonny@example.com".

So LDAP looks for (uid=%u) which then is (uid=jonny@example.com).

Postfix is sending this via the virtual stack so the virtual part is set up like this:

virtual_alias_maps = ldap:/etc/postfix/ldap/ldap-aliases.cf
virtual_gid_maps = static:5000
virtual_mailbox_base = /
virtual_mailbox_domains = ldap:/etc/postfix/ldap/virtual_domains.cf

virtual_mailbox_maps = ldap:/etc/postfix/ldap/ldap-accounts.cf
virtual_minimum_uid = 5000
virtual_transport = lmtp:unix:private/dovecot-lmtp
virtual_uid_maps = static:5000

What I expected is that postfix is using the virtual_mailbox_maps to lookup the user and pass that user to the LMTP so dovecot can do a userdb lookup. Since postfix does not know how to do it and i don't find a virtual_map* parameter that could do it, I don't know what the correct procedure would be.

Should postfix lookup the user via LDAP and send it to LMTP? Or should LMTP do a lookup on base of the recipient email address?

EDIT: I should add that the IMAP part of dovecot works fine when i connect with a mail client to receive the mail. It correctly looks up everything based on my login name which is uid. This of course is possible since when I login to IMAP I pass my uid so its easy to use it for dovecot.

I somehow have to tell dovecot to do it differently when postfix is using it...

/etc/dovecot/dovecot-ldap.conf.ext

hosts = localhost
dn = cn=linagent,ou=people,dc=example,dc=org
dnpass = SECRET
tls = no
auth_bind = yes
base = dc=example,dc=org
deref = never
scope = subtree
user_attrs = \
  =home=%{ldap:homeDirectory}, \
  =uid=5000, \
  =gid=5000, \
  =mail=maildir:%{ldap:mailMessageStore}
user_filter = (&(objectClass=inetOrgPerson)(uid=%u))
pass_attrs = uid=user,userPassword=password
pass_filter = (&(objectClass=inetOrgPerson)(uid=%u))
  • On your last question, I believe only Dovecot should do the LDAP lookup and then send to Postfix whether or not the user exists, as per this document: wiki2.dovecot.org/HowTo/PostfixDovecotLMTP. For your main question, I don't know the answer (yet). – Tommiie Sep 6 '18 at 8:50
  • see my own answer, i don't know it this is the most elegant style though. – tuxmania Sep 6 '18 at 9:20
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I don't know if this is supposed to be like that but I changed the ldap configuration in dovecot like this:

user_filter = (&(objectClass=inetOrgPerson)(|(uid=%u)(mail=%u)))
pass_filter = (&(objectClass=inetOrgPerson)(|(uid=%u)(mail=%u)))

The part where uid=%u I need for authentication from a mail client because the mail client is logging in via UID (username).

The part where mail=%u I need for LMTP receiving from postfix and postfix just knows the recipient mail.

Since uid never is a mail address I guess this solution will work and not creating any conflicts. It also makes sense to me but I wonder why Courier could handle it more elegantly.

I will not resolve the question though since I think it is not the designed way.

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Souldn't you use the %n variable instead of %u?
Check this : https://wiki.dovecot.org/Variables

And this is an extract of https://wiki2.dovecot.org/AuthDatabase/LDAP/Userdb

Variables and domains

User names and domains may be distinguished using the Variables %n and %d. They split the previous username at the "@" character. The previous username is:
- For LMTP, it will be user@hostname, where hostname depends on e.g. the Postfix configuration. - For IMAP, it will be whatever the password database has designated as the username. If the (LDAP) password database has "user_attrs = =user=%n", then the domain part of the login name will be stripped by the password database. The UserDB will not see any domain part, i.e. %n and %u are the same thing for the UserDB.

Thomas

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