Newsletter subscriber problem may occur due to the following reasons:
* Your server time is different then your local time and youâve actually queued the newsletter to be sent a few hours in future and thatâs why itâs not sent right now.
* Magento sent only small part of emails? Donât worry, it will send them out. Magento has integrated limit on the number of emails it can send at once. Eventually, all of your emails will be sent.
* You might need to activate your cron job as itâs often a case cron job is causing you problem. This means you will need to visit this address insert-your-magento-store.com/cron.php manually with your internet browser.
I hope, this info would be helpful for you.