Messages per hour decreasing over time

Hello everyone,

I need your help in order to get to know why the messages/hour decrease over time, it starts at around 508 messages/hour but overtime it decreases to 54 messages/hour; this are my config vars:

define('MAILQUEUE_BATCH_SIZE', 0);
define('MAILQUEUE_BATCH_PERIOD', 86400);
define('MAILQUEUE_THROTTLE', 7);

I think I don’t understand what those vars mean. How do I do in order to keep sending for example 400 messages/hour?. Please help.

Thank you in advance.