Even if you're telling the truth, when your security is compromised, so are all your users' email, because you have full access to it.
Bottom line: Yet another "web 2.x", proprietary, "beta," SaaS, subscription, third-party, unrestricted-privacy-compromising tool without a business model that might be around for a few years before being bought and ruined or going bankrupt. One would have to be nuts to trust it and to build one's business processes around it.
And why? Seriously, it could be done client-side without compromising account credentials or email privacy in a bit of Perl or Python, maybe a browser extension, and throw in some Bayesian analysis to reduce the need for manual templating and scraping. A few hours in Emacs/gnus/etc and no need to hand over ALL OF MY EMAIL to yet another "but we're only storing your patterns!" third-party web site.
Someday people will wake up to the insanity and stop trusting these ephemeral convenience services. The question is, will it happen naturally, or will it take more massive security/privacy breaches before people stop being so lazy and nai...I mean, trusting?