First steps for undelivered system emails:
- Check with the SI Records for notifications and see if there is an error.
- Check your spam folders
- Check to see if other WP emails are being delivered to the email address you used for testing. For example, a password reset for that WP account.
- Check to see if core WP emails are being sent without Sprout Invoices active. For example, a password reset with the plugin (and add-ons) deactivated.
- Check to make sure the email the notification is being sent is not the same email address as your admin account for your WordPress install. Some servers will have issues with this and won’t send the email if the emails match.
If emails are not sent consider using an SMTP service and plugin for your site -
I highly recommend SendGrid because it's free up to 12K emails, that's a lot. Plus they work with email providers to increase deliverability.
Recommended Plugin: WP Mail SMTP
Requires you have an SMTP server/service.