Ask HN: High Volume Email Marketing

We are a software company with about 15 million users (and growing very fast) in Silicon Valley and are having trouble scaling our email marketing campaigns. We will have 25 million+ users by end of month and we can't find a good saas platform to scale with us. Need advice. We are fine with transacation emails (drip emails, autoresponders), but can't find anything good enough for our marketing campaigns.

We tried Sendgrid, we've just temporarily switched to mailchimp right now, but are finding it difficult to:

a. manage large data - uploading a list of 10 million takes about 10 hours+ and is not agile. This sucks.

b. do fast, advanced segmentation of our list based on a dynamic variable such as when we release a feature for 5% of our users, then send. We'd like to just parse this 5% against our master list and quickly send. Or, segment easily using certain variables like license type, sign up date, etc.

c. Easily connect through an API to stop dealing with big data on a website's servers.

d. Robust analytics - we test everything and want to be able to a/b test & get open / click / bounce / manage unsubscribes, etc.

What do high volume senders use? We code all of it our own, just want a sender with a good reputation who handle our advanced segmentation and send well.

Thanks in advance. -m