A family of Microsoft relational database management systems designed for ease of use.
Err, I meant OLE, not OLEDB. When Outlook is set to be the default email program, an OLE command can be used to send an email, but if Thunderbird was the default, the same commands would work against it. Any number of other email programs would be the same deal.
It seems to me that msaccess.exe could be shimmed in there with parameters for the database name, and then code within the database to decode the incoming parameters from the calling application which gives to, from, attachments, subject, message, etc.
Or, finally, if not that, maybe I could write a c# stub that would act as the OLE target, and then pass off the incoming data to the database, if not handle it right within c#, but then, the question becomes, how do I create my own app, and set it as the default email application?