You have completed the DLP installation, and you have added your licensing information, etc.  You have added the Email server information to the SMTP section, but when you click the Save button, nothing happens, and the settings are not saved.

There are no errors in the Localhost logs.

This issue occurs when the connection settings to the SMTP server do not work, resulting in the page making the attempt to connect forever.

If an authentication method is not supported or fails, such as NTLM auth, then DLP cannot use this mail relay. 

To verify this is the issue, try to telnet to the SMTP server from the Enforce server.  The connection will fail if this is the issue.

Make sure the Enforce server is able to connect to the SMTP server with the credentials you have provided in the SMTP Settings.