What is the Newsletter Task Scheduler?
MailPoet adds your emails that are ready to send to a queue.
The task scheduler monitors the queue in order to send your emails in batches according to the sending frequency (X amount of emails every Y minutes) specified in MailPoet > Send with...
The task scheduler has two ways of working:
a) Visitors to your website: every visit (page load) to your website activates the task scheduler script. This is the safest and default method. However, it is not always reliable on website with low traffic.
b) MailPoet's own script: this method does not require anything to trigger it.
It runs automatically as a background process on your website, which ensures that your sending frequency is respected. However, this method can be disable your site to use if you're on one of these hosts.