This article goes over some common troubleshooting steps to make sure system emails are working successfully.
Note: This is used for the System Notification functionality NOT the Notification Service
Verify Settings in the web.config file
Open the web.config file in your website's root folder.
Locate the following section
<!-- SMTP Server configuration -->
<add key="ek_SMTPServer" value="" />
<add key="ek_SMTPPort" value="25" />
<add key="ek_SMTPUser" value="" />
<add key="ek_SMTPPass" value="" />
<add key="ek_SMTP_EnableSsL" value="false" />
For most installs, your ek_SMTPServer and ek_SMTPPort will be the only fields you will need to configure.
Make sure these values are correct, save the web.config and try to send a system notification message.
Testing System Notification messages in the workarea
In the workarea, go to Settings > Configuration > Users.
Find a user that you'd like to send a test email to
Click on the mail icon for that user on the right hand side
Click on the envelope icon on the toolbar and you will be taken to a screen to send the email
Try sending the email. If you receive this email, system notifications are setup correctly. If not your settings may still be incorrect.