I haven't tried this to send mail to external parties as I work on internal ERP (Accounting) systems, but primarily you really just have to change how you think about it. On everything I design email is an "optional", "Under ideal circumstances" tool. For example we have an internal licensing application that we use to generate licenses for our customers. I could notify the licensing department using email - but what happens if it goes wrong? Instead I write to an actual table and have an application sit over it. Lets face it - email is and will always probably be a crapshoot. It just wasn't designed to be terribly reliable and the problem with spam has only compounded that.