searching molecules automatically



 Dear CCLers,
 I apologize if this question is off topic here.
 
I have a batch of molecules, say thousands, in the format of .mol. I wonder if somebody can give me some suggestions about how to search these molecules automatically through databases, such as CAS Registry, or any other type of compound database. I want to see if these molecules exist or not. not necessarily for free.
 thanks a lot!
 Chunhui