Mail couriers are distinguished from ordinary mail services by features such as speed, security, tracking, signature, specialization and individualization of express services, and swift delivery times, which are optional for almost every day mail services. As a premium service, couriers are usually more expensive than standard mail services, and their use is normally limited to packages where one or more of these features are considered important enough to warrant the cost.

Smaller courier services are common, particularly in cities. This type of service finds its niche in smaller packages and documents that need to be transported from one location in a city to another as quickly as possible.