Hi valeriuc,
that’s an interesting use-case I did not think of. Thanks for bringing this up. As of now the plugin does not support your use-case.
For a quick fix, you could modify one line of code yourself. The Job that sends the mails, always sends a batch of mails in one request. The size of this batch is configurable by setting the “Number of emails to be send per request”. When this number of mails was send, the job will be rescheduled to send the next batch at least to seconds later. This interval can be changed manually by editing the following line of code to “add” more than two seconds, e.g. 600 seconds to send the next batch after 10 minutes:
https://github.com/nstaeger/wp-post-email-notification/blob/master/src/Model/JobModel.php#L126
If you do not want to do this on your own, you will need to wait for a future release. I put it on the todo list:
https://github.com/nstaeger/wp-post-email-notification/issues/12
Best,
Nicolai