If you are not receiving e-mail notifications after having set up your WSUS server to send them, you should check both the WSUS server's e-mail setup and the SMTP configuration on the e-mail server.
Troubleshooting the WSUS e-mail setup
In the WSUS administration console, click Options, and then click E-Mail Notifications. On the E-Mail Server tab, check the SMTP server name and port, the sender name and address, and the SMTP server authentication, if necessary. You can use the Test button to verify your settings.
Troubleshooting the SMTP server