A: Tier 3 effectively acts as virtual servers on one server.

You can move servers at any time and it will automatically reset the license on the new server and revoke it on the old server, here's the explanation on how Tier 3 works from the FAQ for Sumo-lings:

https://docs.emaildelivery.com/docs/faq/appsumo-select-faq

What's the difference between Tier 1, 2, and 3?

All 3 tiers on our AppSumo deal have unlimited domains/brands, email delivery connections, contact list size, sending volume, MTAs, you name it, there are no restrictions on any features in the software.

The only difference between each tier is the number of customer accounts and administrator accounts that can be created.

A customer account has access to the email marketing platform, you can use them for your own email marketing or resell customer accounts to others.
An administrator account can add email delivery connections and create customer accounts.

Each administrator account is siloed into it's own environment, and can create customer accounts and manage email delivery connections completely isolated from all other administrators.

This means with a Tier 3 license, it's like running multiple installations of the platform on multiple servers simultaneously, even though it's actually only running on one server. Each administrator account is like giving you another virtual ESP.

Licenses are only valid on one server at a time, if you need to move servers, the license will be revoked for the first server when you use it on the second server.

Tier 3 is a way of getting around this limitation by giving you the same experience of having multiple servers.