<![CDATA[The management of incoming and outgoing mail archives at Madrasah Tsanawiyah Baiturrohim Blimbing is currently carried out manually using physical ledgers and paper-based storage systems. This conventional method results in several administrative problems, including difficulties in searching and retrieving documents, inconsistent letter numbering, delays in the disposition process, risk of document loss or physical damage, and inefficiency in terms of time and human resources. This study aims to design and develop a web-based information system for managing incoming and outgoing mail archives by applying the Sequential Search algorithm as the main search mechanism. The research uses a qualitative descriptive approach with data collected through observation, interviews, and literature review. The system is developed using the Prototype method through iterative stages: requirement analysis, prototype design and development, and system testing and evaluation. The system is implemented using PHP, SQLite, and Bootstrap. Testing of four algorithm scenarios confirms theoretical time complexity: O(1) in best case (1 iteration), O(n) in average case (5 iterations, T(9)=(9+1)/2=5), worst case (9 iterations), and not found case (9 iterations). Black Box Testing across 8 scenarios shows a 100% success rate. The developed system successfully improves the efficiency and accuracy of mail archive management, reduces manual recording errors, and facilitates timely administrative reporting.]]>
