Share an encrypted link with your customer to check the campaign statistics.
Open different admin accounts with different roles. Like reports-only user, newsletter editor, list manager and more.
It is not multi-user. Single installation of files at one domain.
But you may not,
give login access to the customer (in case you manage lists from many different customers).
With the ESP version
Single installation of files at one domain. Your customers (users) have their own accounts. Each account "feels like” the single nuevoMailer.
Your customer has full access to all features. He can design newsletters, manage lists and send campaigns. Only some higher level system tasks are for you as "master administrator” (user accounts, email plans, smtp settings etc).
Of course you can still do all the work or divide the tasks with your customer.
Charging your customer is optional.
With both editions
Sender profiles (from-name, from-email) can be defined at many levels (global, at campaign, at list).
The concept of "tracking domain” can be applied so that newsletter links point to the domain of your choice without actually having the mailer installed at that domain.
Having different standalone installations at your customers' domains. You can do that either with the SB or the MB (1 year subscription license).
You can still do all the work or share some tasks with your customer. You can open different administrators accounts with different roles.
Consider this model when a customer has special requirements about data ownership and access.
It is cost-effective; you have 50% discount for each additional SB license that you order.
Do the math. If you plan to have many installations or want the freedom to install anytime, anywhere consider the MB (1 year subscription license).