Any clues on why my server is deferring email? Here's a dialog from an off network server talking to my plesk server (domains have been changed do protect the innocent):

[root ~]# echo "test email" | mail -v -s "test email 1" tleo@pleskaccount.net
tleo@pleskaccount.net... Connecting to mail.pleskaccount.net. via esmtp...
220 host.servername.net ESMTP
>>> EHLO host.ooffnetworkserver.com
250-host.servername.net
250-AUTH=LOGIN CRAM-MD5 PLAIN
250-AUTH LOGIN CRAM-MD5 PLAIN
250-STARTTLS
250-PIPELINING
250 8BITMIME
>>> MAIL From:
250 ok
>>> RCPT To:
>>> DATA
250 ok
354 go ahead
>>> .
451 qq trouble creating files in queue (#4.3.0)
tleo@pleskaccount.net... Deferred: 451 qq trouble creating files in queue (#4.3.0)
Closing connection to mail.pleskaccount.net.
>>> QUIT
221 host.servername.net
[root ~]#

check the perms/owners on the qmail queue...likely something is wrong there..or you have a diskspace issue. If that isn't the issue, then next thing to check is perms/owner for /var/qmail/bin/qmail-queue

Hi,
I had the same pb , solved by changing perms & owners info to :
-rws--x--x 1 qmailq qmail 15464 2004-11-09 12:19 qmail-queue

This worked for me: chmod u+s /var/qmail/bin/qmail-queue

Any one knows what is the cause of this problem?

I mean, everything was working fine, but out of the sudden I have to change permisions for this file to get it working again.

I don't know why, but Plesk overwrites your permissions on a semi-regular basis. I'd assume that it's for security, but it gets some of them wrong. I've asked customer support if there's a way to make it stop overwriting my qmail-queue permissions. I'll post the responce (if it's helpful) when I get it in a few hours.

Ev1Servers' responce was that there is no way to stop Plesk from doing this.

Fixing perms according to the proposed
chmod u+s /var/qmail/bin/qmail-queue
solved also the issue for me. Thanks

(btw it was on a RHEL4, QMAIL installed according to qmailrocks procedures, no plesk involved with this machine).