It looks like slapd server is overwhelmed with too many requests at the same time, which makes postfix getting timeouts.
On the postfix side hopefully it's only a "temporary lookup failure" but I want to correct that problem.

I would suggest you post to postfix mailing list, together with your "postconf -n" output, and provide details on OS used, Postfix, OpenLDAP versions.

Are you using proxy:ldap: on your postfix ldap lookup tables? (You should.)

On the OpenLDAP side: If you need tuning help, post here your OS, Openldap version details, configuration, backend configuration (if applicable), as well as the content of your openldap data directory.

If you can post stats info, that will be useful too. If you are using BDB/HDB:

   (slapd_)db_stat -m
   (slapd_)db_stat -c

Cheers,
Nick

• I don't even know if I'm using proxy:ldap ? My postfix config is :
• virtual_mailbox_domains = ldap:/etc/postfix/ldap-domains.cf
• virtual_alias_maps = ldap:/etc/postfix/ldap-aliases.cf
• virtual_mailbox_maps = ldap:/etc/postfix/ldap-accounts.cf
  
• slapd_db_stat -m
• slapd_db_stat: DB_ENV->open: No such file or directory
• How can I show the "the content of your openldap data directory" ?

Sorry for these beginner questions !

By the way, some information to begin :

• # uname -a
• Linux hostname 2.6.18-238.19.1.el5 #1 SMP Fri Jul 15 07:32:29 EDT 2011 i686 i686 i386 GNU/Linux
• # cat /etc/redhat-release
• CentOS release 5.6 (Final)
• # slapd -V
• @(#) $OpenLDAP: slapd 2.3.43 (Mar 30 2011 19:59:52) $
• mockbuild@builder10.centos.org:/builddir/build/BUILD/openldap-2.3.43/openldap-2.3.43/build-servers/servers/slapd