A Universal Messenger instance can either be deployed on-premise on your own (virtual) server or on a (virtual) server that is hosted somewhere else.
In addition Pinuts offers a Software as a Service solution that provides a fully customizable UM instance operated off of Amazon Web Services.
This solution utilizes several high level AWS services like
Relational Database Service
Application Load Balancer
Certificate Manager
Simple Email Service
Simple Notification Service
Elastic Container Registry
S3
Secrets Manager
CloudWatch
The SaaS solution usually consists of three separate UM stacks (test, staging and prod) that can be configured and updated independently.