[GordonS]

I agree with this - for desktop software, a perpetual license and optional annual maintenance is the expected model. Moreover, this seems to me to be a tool you'd use once to create a template, and then your content gets slotted dynamically into.

As some pricing feedback, I'd personally prefer to pay something like $75-85 as a one-time fee, with $20-30 optional maintenance to get access to the latest version and continued support - $20/month is way too high; yes, creating nice emails that work across clients is a PITA, but there are some very popular OSS templates out there that work great.