Microsoft Dynamics CRM Online allocates an initial 5 GB of storage. This storage is pooled and shared by all service users. In addition, a company may purchase more Microsoft Dynamics CRM Online storage in gigabyte increments charged monthly, currently USD 9.99 per GB per month. Storage is shared across the organization and is not a per-user add-on.
To check the database storage usage:
If you get close to the limit of your storage space, several ways to reduce the amount of space used exists:
Read more in this article: 10 ways to free storage space in Microsoft Dynamics CRM Online
Is there a way to manage email tracking with attachements to store the attachements on Sharepoint?