This is the Bangladesh postcode website, including more than 1,349 items of division, district, sub-district and zip code etc.
DivisionDivision is the first-level administrative division in Bangladesh. Each division is further split into several districts. In postal system, the previous seven first-level administrative still being used, but in fact, Mymensingh was added as the eighth division in 2015.
For more explanation, please read the official document: BGD.pdf (English)