This monorepo contains different implementations of MessagePickupRepository interface for Credo agents, currently in use by 2060.io DIDComm Mediator
This is the simplest one: a fully featured implementation that supports Message Pickup V2 in a multi-instance environment and only requires a PostgreSQL database, which could be on the same host than Credo's wallet. Check out its documentation here.
A more advanced development where every Credo instance is connected through a WebSocket with a Message Pickup Repository Gateway that handles all the coordination between instances and aims to provide a better performance in large scale deployments where a big message throughput is required. Check documentation of both the client that must be injected into each Credo Mediator instance, and the server itself, for more details.