On a Plesk server, the maximum size for an individual e-mail sent through qmail is unlimited. You can limit this size by adding a number to the /var/qmail/control/databytes file.
If you wanted to limit this to something like 10MB, you can just run the following command:
echo “10485760″ > /var/qmail/control/databytes
This will limit the size of messages (including attachments) to 10MB as a maximum.
I really dislike qmail. But, since I use Plesk, I’m stuck with it. However, I found a way to improve it’s awful mail queue performance by putting the mail queue onto a ramdisk. This is actually pretty darned easy to do.
First, toss a line like this into your /etc/fstab:
none /mailqueue tmpfs defaults,size=100m,nr_inodes=999k,mode=775 0 0
This will make a 100MB ramdisk on /mailqueue. Now, just symlink /var/qmail/mqueue to /mailqueue and move your e-mail over:
# mount /mailqueue
# chmod 750 /mailqueue
# chown qmailq:qmail /mailqueue
# mv /var/qmail/mqueue /var/qmail/mqueue-old
# ln -s /mailqueue /var/qmail/mqueue
# rsync -av /var/qmail/mqueue-old /mailqueue
This has significantly cut the iowait on my server during heavy e-mail periods. In addition, tools like qmHandle now fly through my mail queue and give me reports very quickly.
If you have a new Plesk installation and the following option is greyed out in Server -> Mail:
Switch on spam protection based on DNS blackhole lists
Just install the following RPM from Plesk:
psa-qmail-rblsmtpd
I stumbled upon this peculiar bounce message recently while working on a server:
Hi. This is the qmail-send program at yourmailserver.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
<user1@domain.com>:
This message is looping: it already has my Delivered-To line. (#5.4.6)
--- Below this line is a copy of the message.
Return-Path:
Received: (qmail 14418 invoked by uid 110); 9 Jan 2008 13:04:33 -0600
Delivered-To: 54-user2@domain.com
Received: (qmail 14411 invoked by uid 110); 9 Jan 2008 13:04:33 -0600
Delivered-To: 53-user1@domain.com
Received: (qmail 14404 invoked from network); 9 Jan 2008 13:04:33 -0600
Received: from otherdomain.com (HELO otherdomain.com) (11.22.33.44)
by yourmailserver.com with SMTP; 9 Jan 2008 13:04:33 -0600
Basically, this is qmail’s way of letting you know that your e-mails are stuck in a mail loop. One e-mail user is redirecting to another e-mail user, and that e-mail user is redirecting back to the first one. If q-mail already has a delivered to line which matches one that it already added, it bounces the e-mail and halts delivery.
I stumbled upon a server running Plesk 8.2.1 where a certain user could not receive e-mail. I sent an e-mail to the user from my mail client, and I never saw it enter the user’s mailbox. It didn’t even appear in the logs.
After checking the usual suspects, like MX records, mail account configuration, and firewalls, I was unable to find out why it was occurring. Even after a run of mchk, the emails would not be delivered.
I began testing with a telnet connection to the SMTP port:
$ telnet 11.22.33.44 25
Trying 11.22.33.44...
Connected to 11.22.33.44.
Escape character is '^]'.
220 www.yourserver.com ESMTP
HELO domain.com
250 www.yourserver.com
MAIL FROM: test@test.com
250 ok
RCPT TO: someuser@somedomain.com
421 temporary envelope failure (#4.3.0)
QUIT
221 www.yourserver.com
Connection closed by foreign host.
Temporary envelope failure? I was still confused. After reviewing the logs, I found the following line whenever I tried to telnet to port 25 and send an e-mail:
Dec 2 00:15:49 www relaylock: /var/qmail/bin/relaylock: mail from 44.33.22.11:17249 (yourdesktop.com)
It turns out that the customer was using greylisting in qmail with qmail-envelope-scanner. After a quick check of /tmp/greylist_dbg.txt, I found the entries from me (as well as a lot of other senders), and that ended up being the root of the problem.