Reading When I'm Gone and thinking how much easier it'd be to pull this thing off with Google Apps Script. A spreadsheet with dates and pre-written email messages. A trigger to run daily and check if there's a message to be sent. Additional script logic for recurring events, "Happy {N}th birthday", holidays, etc. It's not like those are very original to begin with.

@Elias Yeah, 3 year old spam. Clever linking