Email Subscribers can and does indeed send emails in background. That can happen if your WordPress setup / webhosting support it though.
We have extensive documentation on this. Please refer to:
There are further links in these articles about setting up crons with cPanel etc.
If you have difficulty with any of these, you can also sign up for our paid Starter plan, that takes care of managing automatic email sending (among many other things) at a very affordable price.
The “Send” button is the “last resort” – if everything is failing, or if you want to manually dispatch emails at any time, then only you’d use it.
Most users setup automatic background sending and do not have to press the send button.
Please check under your email sending settings if everything is setup properly. Do setup cron – at least WordPress cron (it’s not that hard). Contact your hosting company about this and they can also help. Or signup for any of our paid plans. That should solve this problem.
Hope this helps.