Out-of-the-box installations of Drupal use the server's default "php sendmail" process to transmit email notifications from the website.  Most web-hosting providers do not allow website owners to configure the "php sendmail" process to use an authenticated email account.  As a result, such email notifications are often flagged as spam (although the From name and address might read a legitimate name and email, the actual email sending the message does not match up).

To circumvent this issue, the SMTP Authentication Support module is installed/enabled on many Drupal websites.  This allows the website to use a legitimate email account to send its notifications/emails.

To configure the SMTP Email account for your website, go to Configuration > System > SMTP Authentication Support.  Most of the settings can be found from your email provider's help section.