Email notifications not sent

Assuming that the issue is indeed limited to e-mail messages (i.e. the reservations are correctly displayed in Reservations tab) then the plugin is not directly responsible of email delivery, as it triggers the WordPress core functions to send them using the best practices to do so.

The culprit lies elsewhere, and here are a couple of suggestions to fix it:

Install an SMTP plugin

As the PHP mailer used by your server can be unreliable, you are strongly invited to install the free and powerful WP Mail SMTP plugin or the equally valid Post SMTP Mailer.

Those plugins reconfigure the wp_mail() function to use SMTP servers instead. You can use a very reliable SMTP server like the Google one. This should minimize any server-related e-mail issue.

Check the error.log file of your server

Read the error.log file of your server (this is a general advice about any issue you may have). If you don't know how to retrieve it, just ask to your hosting provider. Or drop a message to our support.

Check the sender address

Check the admin e-mail address that your WordPress general settings displays. It should belong to your domain, otherwise it can be blocked due to security policies by your server.

Check the junk mail

Last but not least, be sure that the email is not sent for real, rather than thrown into the SPAM folder by the e-mail client.