Bear in mind that the email address which you are using for “Mail from” must be of type [email protected] and must also be same as the smtp username in the setting.
Ok let's dig in already!!!
Step 1: Log into your Joomla Dashboard.
Step 2: In the top menu, hover over System and then click Global Configuration.
Step 3: Click the Server tab.

Step 4: Under Mail Settings, configure the following settings and then click Save:
From Mail: email address created in cpanel
From Name: Name of your Company
Mailer: SMTP
SMTP Port: 25
SMTP Authentication: Yes
SMTP Security: None
SMTP Username: email address created in cpanel
SMTP Password: password for your email address //password of email above
SMTP Host: localhost
Step 5: Click on save on the Menu bar.

Step 6: You can now click on SEND TEST MAIL from the configuration page to confirm that the settings are working perfectly.
You should get a response as below for a successful set up.:
Congratulations, your Joomla website is now configured to use SMTP! Be sure to test your site and ensure emails are sending properly