The rapid growth of cross-border E-commerce (CBEC), driven by major Asian E-tailer platforms, results in significant operational challenges for domestic parcel networks. These networks are not designed to handle volatile parcel flows, which results in network instability. This study addresses the question of how to mitigate this network instability within PostNL's network. By adopting the Design Science Research (DSR) approach, the paper systematically moves from identifying the systemic root cause of network instability to designing and evaluating strategies that mitigate this instability. The methodology integrates qualitative and quantitative methods, including process mapping, data analysis, and Causal Loop Diagrams, to establish a dynamic hypothesis. Subsequently, a portfolio of four distinct mitigation strategies is designed and evaluated using a quantitative process simulation model across various volume scenarios. The findings reveal that the primary driver of instability is not the external variability of CBEC flows, but the system’s internal reinforcing backlog loop. Furthermore, the quantitative evaluation demonstrates that strategies directly targeting this feedback structure are most effective. Specifically, interventions that manipulate timing constraints to weaken the backlog loop have a significant effect in reducing backlogs, while strategies targeting linear process inefficiencies have a minimal effect. The research concludes that postal operators should shift from reactive processing to proactively managing their underlying feedback structure. It provides a validated dynamic hypothesis for network instability and a portfolio of mitigation strategies, the primary artefact. Together, these outputs demonstrate the successful application of a multi-method DSR approach for solving complex problems in logistics.