Setting the maximum mail size in qmail

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.
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Reduce iowait in Plesk: put qmail’s queue on a ramdisk

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:
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Can’t enable DNSBL/RBL in Plesk because it’s greyed out

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
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qmail: This message is looping: it already has my Delivered-To line

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.</p> Return-Path: <remoteuser@otherdomain.
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Plesk and qmail: 421 temporary envelope failure (#4.3.0)

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.
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