==== Required information ====
- iRedMail version: 0.8.6
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP (Samba4.1.3 AD)
- Linux/BSD distribution name and version: FreeBSD9.2
- Related log if you're reporting an issue:
====

Very often i see the same in maillog

Jun  5 17:38:10 gate postfix/cleanup[40342]: 27405357B: message-id=<e48954c1081f36d4af03c81d042bef2a@domain.com>
Jun  5 17:38:10 gate postfix/qmgr[38579]: 27405357B: from=<user1@domain.com>, size=438, nrcpt=1 (queue active)
Jun  5 17:38:10 gate roundcube: User user1@domain.com [192.168.1.193]; Message for user2@domain.com; 250: 2.0.0 Ok: queued as 27405357B
Jun  5 17:38:10 gate amavis[39574]: (39574-02) loaded policy bank "MYNETS"
Jun  5 17:38:10 gate amavis[39574]: (39574-02) (!)lookup_ldap: do_search: failed: LDAP_OPERATIONS_ERROR
Jun  5 17:38:10 gate amavis[39574]: (39574-02) (!!)TROUBLE in process_request: do_search: failed: LDAP_OPERATIONS_ERROR at (eval 148) line 538.
Jun  5 17:38:10 gate amavis[39574]: (39574-02) (!)Requesting process rundown after fatal error
Jun  5 17:38:10 gate postfix/smtp[40343]: 27405357B: to=<user2@domain.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=1.2, delays=1.2/0.01/0/0.01, dsn=4.3.2, status=deferred (host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))
Jun  5 17:38:10 gate postfix/smtpd[40338]: disconnect from localhost[127.0.0.1]

I see this error up to 3 times for 1 e-mail and recipient can get it after 10-20 min.
"amavisd restart" solve the problem for 30 min only.

Part of amavisd.conf

# Integrate Amavisd-new with OpenLDAP.
$enable_ldap    = 1;    # 1 -> enable, 0 -> disable.
$default_ldap   = {
    hostname        => "ads.domain.local",
    port            => 389,
    version         => 3,
    tls             => 1,
    inet6           => 0,
    timeout         => 120,
    base            => "ou=personal,dc=domain,dc=local",
    scope           => "sub",
    query_filter    => "(&(objectClass=amavisAccount)(mail=%m))",
    bind_dn         => "cn=vmail,dc=domain,dc=local",
    bind_password   => "pass",
};