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:
Should you find yourself needing to send e-mail destined for a certain account to a blackhole or to /dev/null, you’ll find very little information from Google.
When Plesk is installed, the default certificate for the Plesk interface itself is a self-signed certificate that is generated during the installation.
If you find that Horde (with Plesk) keeps refreshing when you attempt to log in, and there are no errors logged on the screen or in Apache’s logs, check the session.