gmail sender tool

I am producing a tool for my personal use which allows SMTP traffic to be relayed over TLS to gmail. Basically it will allow you to use any tool which supports SMTP but not SMTP over TLS to send email over gmail. I am considering releasing it as a commercial product, ie $100 per 200k emails sent or a license for X concurrent gmail addresses.

I want to get a feel for what other functionality and what sort of demand for that sort of software there would be. Anyone who does respond may be considered for beta testers or to vouch for the software.