Comment by procaryote

I like the general idea, but unless you're assuming some very clever language or even more clever ORM that fixes things implicitly, wouldn't

    email.bulkSend(generateReminderEmails(getExpiredUsers(db.getUsers(), fiveDaysFromNow)));

get all users and then filter out the few that will expire in 5 days, on a code level? That doesn't sound like it would scale