Limitations of SharePoint 2010 Sandboxed Solutions

1. No SPSecurity – RunWithElevatedPrivileges cannot be used inside Sandboxed Solutions.
2. No GAC Deployment – It can't be deployed to Global Assembly Cache(GAC)
3. No Email Support - No support to SPUtility.SendEmail namespace for sending mails.
4. No Visual Web parts can be deployed
5. No Global folders access– No access to folders like “_layout” & “resources”.
6. Can be only Deployed at site collection level and sub site level.
7. No Feature stapling – New Feature cannot be added to the existing Feature.
8. No custom Timer jobs
9. ADO.NET connectivity cannot be implemented and you cannot directly connect to a database.
10. No access to taxonomy fields.
11. You can't read or write from/to web.config file.
12. No full trust solutions can be deployed.
13. Accessing the Objects in another Site Collection.
14. No support to Microsoft.SharePoint.WebPartPages namespace.
15. Making web service (external) calls over the internet, or accessing code that is not marked to allow partially trusted callers are not supported.