Various industrial and business sectors use Software-as-a-Service due to its fast services. However, Software-as-a-Service providers face various challenges in providing high-quality services while simultaneously managing vast multi-tenant infrastructure models and increasingly complex user requirements. To address these problems, we identified those factors that affect the quality of Software-as-a-Service from the perspective of provider–user relationship and investigated how service providers can objectively improve user satisfaction. In a case study, we evaluated the perceived service quality of an information system in the public sector based on user satisfaction with the quality of external outsourcing service in terms of assurance, empathy, responsiveness, reliability, and communication. We identified new sub factors (commitment, skills, effectiveness, change management, business processes, and motivation) and proposed action steps that can guide best practices in ensuring Software-as-a-Service quality. These factors are greatly influenced by the communication between providers and users.