[kh99]

There was a mod for sending mail using "cron" (actually, vb scheduled tasks), but the mod is now built in to 4.2.1. You can turn it on by setting "Use Cron Based Sending" to Yes (under Email Options). By default the scheduled task runs every 10 minutes, so you can set "Number of Emails to Send Per Batch" to 1/6 of what you want to send per hour. Some important emails bypass the queue, so if your host is very strict then you'd want to set the number per batch to a little less than 1/6 to allow for those.

That feature processes the queue in the order the messages were generated, so it doesn't do anything special like cycle through all members.