Hello, The needs that you're describing sound like they'd best be served through our Constant Contact Partner Program, you can find more information at http://www.constantcontact.com/partners . This will allow you to provision separate accounts for each of your 50 users. Separate accounts will allow them to keep their lists discrete from one another, as well as allowing them to each have their own 'from' and 'reply-to' email addresses and email footers. We also have several integration options available to partners as well as webhooks to allow push notifications. If you don't need your users to log in directly, or if their lists do not need to be discrete from one another, you can certainly allow multiple users access to your account (and their own list or sets of lists) via an integration using the API, but you're right. Our API does not currently deal with segments, though without access to the log in of the account, your users' lists would not be easily visible one another.
... View more
