First and foremost, I would like to thank my doctoral advisor, Prof. Dr. Richard Pibernik, for his excellent supervision. I am extremely grateful for his continuous support and guidance along the journey that led to this dissertation. His insightful suggestions and constructive criticism in numerous deep and fruitful discussions enriched my work and enabled me to develop early ideas and findings into solid results.I would also like to thank my second advisor, Prof. Dr. Christoph Flath, for the many insightful comments, useful hints, and challenging questions that not only opened up new perspectives but oftentimes led to a new avenue for further investigation that helped to improve my research.Furthermore, I would like to thank all colleagues at the Chair of Logistics and Quantitative Methods in Business Administration and the Chair of Information Systems and Business Analytics for the stimulating discussions and the valuable feedback during our OPIM seminars, and in particular Peter Wolf for the great collaboration on our research article. Thanks for all the chats at the coffee machine, for all the fun during our retreats and the legendary Christmas celebrations, and for making this journey such a great experience.Finally, I would like to express my gratitude to my family and especially to my wife, who always encouraged and supported me in a loving way. I am deeply grateful for her endless patience and loving care throughout this journey.vContents 4.4.3 Mail Sorting Capacity-A Two-Stage Capacity Planning Problem .