Problem with too many concurrent LDAP requests (Postfix+LDAP)

["Denis BUCHER (lists)" <dbucherml@hsolutions.ch>]

Dear all,

I am using LDAP as backend for Postfix for all email accounts. Any email coming to the server is checked against LDAP to check if email is valid, and deliver it accordingly.
It works almost perfectly but I have a big problem that arise when receiving (or sending) too many emails at the same time.

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.

In the logs I get two kind of LDAP errors :
a)

• postfix/trivial-rewrite: warning: dict_ldap_lookup: Search error -5: Timed out
• postfix/trivial-rewrite: fatal: ldap:/etc/postfix/ldap-domains.cf(0,lock|fold_fix): table lookup problem

b)

• postfix/smtpd: warning: dict_ldap_connect: Unable to bind to server ldap://localhost:389 as cn=mailadmin, ou=mailservices, dc=domain, dc=ch: -5 (Timed out)

If someone had a suggestion on how to optimize the LDAP server to be able to cope with the demand coming from postfix it would be great !

Denis