BookLibary Component for send email use mail functions and configure from Joomla Global setting.
Please try send any email from Joomla, test email with help mass mail function.
Follow below documentation:
First of all you need configure Joomla mail settings.
Log into your Joomla Dashboard.
In the top menu, hover over Site and then click Global Configuration.
Click the Server tab.
Under Mail Settings, configure the following settings and then click Save: Mailer. ...
If you do that and still will have problems, give us
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