how many user can the plugin handle ?

Hi mndo123,
Thanks for your message.

WordPress struggles when doing anything that big due to not being able to run any background tasks concurrently. I have plans in the roadmap to implement some improvements to how emails are sent out and notifications are saved when there are large amounts of users but it’s a little way off yet.

For the time being, I recommend trying to send to smaller groups or sending out multiple notifications of the same type that handle different user roles to see if this helps.

Hope this helps.

Thanks,
Jack