I understand completely. Unfortunately, the changing landscape of email today, in the face of spammers, has made what you are doing pretty difficult to outsource anymore. I don't know of any reputable third-party service that still does this kind of thing, or I'd be happy to point you to them.
This is one of the reasons that more and more of the kind of synopsis communication you are talking about is now done via RSS subscriptions and folks who follow these kinds of activities are beginning to rely so much on the feeds.
Even if you set up and use your own mailservers to send the mail, and your subscribers want to receive it, many of the large ISPs just refuse to accept and deliver this kind of mail reliably, as it can be very difficult to stay of everyone's blacklist.
Even our own status blog, which would be a perfect example of a legitimate use of this kind of an email (you subscribe to a synopsis for a daily update) has moved to a purely RSS notification model (and did so quite a long time ago).
I suggest looking at RSS for the way to do this. It is the way the future is going, and the pain of converting those email subscribers to RSS feed subscribers is less, I feel, than the pain by trying to keep mass mailing subscribers every morning (which is only get to get harder as time goes on).
Email just isn't the best way to do this anymore. I'll grant you, it is a hard change to adapt to, and some readers will resist, but with some things change is inevitable.
I think that until "email" as we know it is "fixed" (if that is even possible) RSS, or other syndication formats, is the best way to go today to keep large numbers of people regularly informed.
--DreamHost Tech Support