451 4.4.1 timeout writing message to mail.ourdomain.com.: Broken pipe

[diadem.support]

There are some problem in the incoming mail in Linux (Red Hat Enterprise Linux Server release 5.2) Plesk 8.6 with qmail, below are the Server logs

Mar 20 06:34:12 dns2 spamdyke[20669]: FILTER_SENDER_WHITELIST sender: [email protected] file: /var/qmail/spamdyke/whitelist_senders(6)
Mar 20 06:34:14 dns2 spamdyke[20669]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 06:34:14 dns2 spamdyke[20669]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 06:34:14 dns2 spamdyke[20669]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 06:42:54 dns2 spamdyke[20669]: TIMEOUT from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown) reason: TIMEOUT
Mar 20 11:05:49 dns2 spamdyke[17521]: FILTER_SENDER_WHITELIST sender: [email protected] file: /var/qmail/spamdyke/whitelist_senders(6)
Mar 20 11:05:52 dns2 spamdyke[17521]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 11:05:52 dns2 spamdyke[17521]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 11:05:52 dns2 spamdyke[17521]: ALLOWED from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown)
Mar 20 17:22:42 dns2 spamdyke[17521]: TIMEOUT from: [email protected] to: [email protected] origin_ip: *IP Hide* origin_rdns: smtp.domain.com.np auth: (unknown) reason: TIMEOUT

Below are the Server details

Plesk Control Panel version: psa v8.6.0_build86080930.03
OS: RedHat el5Operating systemLinux 2.6.18-92.1.18.el5PAE
Anti SPAM solution
Spamassassin 3.2.5-4
qmail-scanner 2.02-1
clamav 0.94.2-1
spamdyke 4.0.10

The client are getting bounce mail as below, they are using Sendmail 8.13.8/8.13.8.

The original message was received at Thu, 19 Mar 2009 17:30:20 +0545
from corporate227_12.domain.com.np [*Some IP*] (may be forged)

----- Transcript of session follows -----
451 4.4.1 timeout writing message to mail.ourdomain.com.: Broken pipe
<[email protected]>,<[email protected]>,<[email protected]>... Deferred
Warning: message still undelivered after 4 hours
Will keep trying until message is 1 day old

We have set Spamdyke Timeout 5 min. Can anybody help us in solving this issue?