Microsoft Dynamics Marketing is scheduled to be retired on May 15, 2018. After that date, the service will not be available. Please plan accordingly. Microsoft has already introduced the successor of Microsoft Dynamics Marketing: Microsoft Dynamics 365 for Marketing, which is available in preview.

For further information about the retirement of Microsoft Dynamics Marketing, please visit
https://technet.microsoft.com/en-us/library/mt815204%28v=mdm.19%29.aspx