If you are using Outlook 2013 and the Save to CMS button used to be on your ribbon but it has disappeared.
In this scenario check that the CMStoOutlook addon has been disabled.
Click file on the menu bar, and check to see if there is a "disabled Add-on's" on the bottom of the screen. If this appears, click the button and you will be shown a list of Add on's which are currently disabled, if CMS to Outlook is disabled you can enable from this screen.