[gyardley]

I use MailChimp's STS - really just a wrapper on top of Amazon's SES. I might just use SES if I wasn't already running newsletters through MailChimp, although MailChimp's wrapper is nice.

The only event-driven emails I'm currently sending line up pretty well with Stripe's events, so I'm just detecting them when they're sent from Stripe to my server, and firing off emails when they arrive. But if I wanted to set up a drip campaign like you've suggested, I'd just set up a daily cron job.