The aim of this diploma thesis is to study the methodology of Domain-Driven Design (DDD) and apply it to the design and implementation of a communication module for internal messaging between agents in the LiveAgent software. The thesis will begin with a detailed review of DDD theory, including its core principles and practical applications in software architecture. It will also cover the challenges of working with legacy systems and the role of refactoring in improving codebases. Based on this theoretical foundation, the existing instant messaging functionality in LiveAgent will be restructured using DDD principles to improve the system’s modularity, maintainability, and scalability. The focus will be on clearly separating domain logic from technical infrastructure to facilitate easier system maintenance and future enhancements. The outcome of this work will be an implemented module and a technical report documenting the design process, implementation, and results.