11:49 Feb 2 

May I ask for who you are translating? UK/US? It will be a little tricky to find a generic term to fit all scenarios, so I guess registered mail would be the best of the bunch. Just so you are aware, in the UK, special delivery is a service offered by Royal Mail that, in theory, guarantees a next (business) day delivery with online tracking and it is to be signed for on delivery by the recipient or a member of the household to where it is going. Compensation is also offered should the guarantee not be upheld.

11:06 Feb 2 

Wikipedia: "In the United Kingdom, up until the 1990s, the Royal Mail provided a "Registered delivery" service now replaced by "Royal Mail Special Delivery", which provided extra security and insurance against loss (often using special stamps, postmarks and blue lines)."