That's still not answering the question though. I don't know of any bulk email provider who doesn't allow you to export and import your lists via an open format like csv.
> It's a general comment on the professionalism of the bulk email delivery industry, namely there is none.
I strongly disagree. I’ve had the chance to speak with numerous deliverability folks who work at esp’s over the years and they’ve all for the most part been incredibly professional and helpful.