The Hermes Express is the Olympian equivalent of a courier/messenger service, run by @Hermes.

History

Quest for the Master Bolt

@Percy Jackson uses the Hermes Overnight Express to send the head of @Medusa back to @Olympus after he beheaded her in the battle at @Aunty Em's Garden Gnome Emporium. Later, he finds the same package in his bedroom marked "Return to Sender" sent back by @Poseidon.

Quest for the Athena Parthenos

When @Annabeth Chase is on her quest for the @Mark of Athena under the city of Rome, she stumbles across a box from Hermes delivery services. She is excited, because it may be something to help with her quest. When she opens the crate, however, all that is left inside is bubble wrap. Annabeth later realizes it was a gift and uses it as gauze for her broken ankle.

Quest for Ganymede's Chalice

Percy suggests just using Hermes Express to send @Ganymede's @Olympian Chalice back to the godly cupbearer, recalling that Hermes Express has one-hour delivery in @Manhattan. However, Ganymede needs his chalice immediately and, as the leader of the quest, it's Percy's job to hand deliver the chalice as per the rules regarding quest completion.