While configuring Magento 2 SMTP extension, it is important to enter the host details correctly. First, the admin will select the hosting provider. Then, the email ID (username) and password of that host are entered for Magento 2 SMTP extension. These details are required to establish a connection to the SMTP server. After entering the correct details, the admin can send a test mail to confirm if the settings are working properly.
Check out more details at: http://webkul.com/blog/smtp-configurator-magento2/