We suggest trying one of the following:
⋅ A － Contact your hosting server support and see if the mail server is enabled for your site. If this is not the case, they should simply enable your mail server and this will resolve the issue.
⋅ B － Contact your hosting server support and check if the SMTP username and pass are set for your site. If these are set and the issue persists, then you need to install this plugin.
Once you set the parameters (user and pass) you will be able to send emails properly and the issue should be resolved.