Which big ones use that as their white label?

Cox, Comcast, Roadrunner, etc. Most of the large ones besides Gmail.

Thanks - that's why I use sendgrid & mailchimp. Don't have time to care about these things.

Don't know why you're being downvoted; any business <$1M annual revenue that has to send loads of e-mail shouldn't be wasting time rolling their own solutions

We do more than that, but only send a few hundred emails per day outside of our internal google apps accounts (using sendgrid) and then blast a newsletter once a week via mailchimp.