Duplicated newsletters

If your MailPoet plugin is sending newsletter duplicates to your subscribers, your website is probably getting high levels of traffic and your MailPoet Cron option is deactivated.

The path to enable MailPoet Cron is at  Settings page >  Advanced tab > Geeky Options link.
Free Users:

Premium users:

Want to understand what a "Cron" is? Read here: Understanding the Cron