SSL varies by service and is available for Email, Chat, Calendar, Docs, and Sites. Please note that SSL access is not available for Google Video for Business or the Google Talk desktop client.
The advantage of SSL is added security for your users. If your users access Google Apps on a non-secure Internet connection, such as a public wireless or non-encrypted network, your users’ accounts may be more vulnerable to hijacking. A secure connection prevents hijacking by protecting the cookie session. Cookie session hijacking refers to a situation where an impostor gains unauthorized access to cookies and seizes control of a legitimate session while it is still in progress.
However, forcing HTTPS for your users can make Gmail a little slower. Also, please note that, if you enable SSL, you will not be able to see your mail in the Gmail gadget on the Google Apps Start Page since it is not served over SSL. If you trust the security of your network, you can turn this feature off at any time. When the feature is disabled, your users will access Google Apps via HTTP (Hypertext Transfer Protocol).
Sign in to the Google Apps administrator control panel.
Click Domain settings.
Under the General tab and in the SSL section, check the box next to Enable SSL.
Click Save changes.
Note: If you force HTTPS, your users won’t be able to disable HTTPS on an individual basis. However, if you don’t force HTTPS, your users can enable HTTPS when necessary but only if you also have enabled the Enable pre-release features check box in your Google Apps control panel.