The reason for these departments is to maintain the secrecy of correspondence ("brevhemlighet"). This department is the only one within the postal service that

The reason for these departments is to maintain the secrecy of correspondence ("brevhemlighet"). This department is the only one within the postal service that has the right to open mail and try to decode who is the recipient. The rebuse or other shenanigans is not the majority of letters, but unreadable handwriting, wet or in other ways damaged so the recipient cannot reliably be established.