[kh99]

In the admincp under Settings > Options > Email Options, if you have Use Mailqueue System and Use Cron Based Sending set to Yes, then you want to make sure you have a reasonable value for "Number of Emails to Send Per Batch". The scheduled task for cron based sending is called 6 times per hour, so you should set the batch size to 1/6 of the number of emails to send per hour (if your host specifies a limit), or to some reasonable value if you have no limit (see the help for "Use Cron Based Sending" in the admincp).