Actually, I'm looking for a service that allows me to:

- test whether emails I send actually end up in the inbox of my customers (not in their spam filter)

- buffer outgoing generated email, such that I can review them before they are really sent (or send them if I don't review them within say 48 hours)

Also, isn't there some open source validation tool, that can also convert any valid HTML into HTML that is accepted by all/most clients?