Setting the maximum mail size in qmail
On a Qmail 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.
Forcing qmail to process e-mail in the queue
Normally, qmail will be able to process the mail queue without any interaction from the system administrator, however, if you want to force it to process everything that is in the queue right now, you can do so:
kill -ALRM `pgrep qmail-send`
If for some peculiar reason you don't have pgrep on your server, you can go about it a slightly different way:
kill -ALRM `ps ax | grep qmail-send | grep -v grep | awk '{print $1}'`
Your logs should begin filling up with data about e-mails rolling through the queue.
mchk: Unable to initialize quota settings for someuser@somedomain.com
If you're working in Plesk and you receive this error:
mchk: Unable to initialize quota settings for someuser@somedomain.com
Run this command to fix the issue, but be patient:
find /var/qmail/mailnames -type d -name '.*' ! -name '.spamassassin' -ls -exec touch '{}'/maildirfolder \; -exec chown popuser:popuser '{}'/maildirfolder \;