I don't really know how slow/fast it is - as I still don't have large list (just few emails, mostly mine and few friends) that I use for testing.

Anyway, in the control panel of application, when you create an email and place it in outbox, you can select the date & time when to send that particular email. I did it that way, so someone could prepare say several issues of newsletter, before they are to be sent. Obviously cron is set to run every hour or so, a script that checks if there are some emails in outbox that need to be sent. And there is no direct action performed by user ...

So to answer your question - no my goal is not to notify when all emails are delivered (it's an option - it sends email when it finishes if you want it of course).

And by my logic - if my application forwarded it to the SMTP server then my part of job is done - so it can send the notification.

If this speed-up can only be done by using qmail/sendmail type applications and not SMTP server directly - then it's fine with me. In my features I will write the opposite. Kind of : "If you use Open Source OS you get a special bonus - faster sending of emails." :)