Communication Service
The Communication Service is responsible for permanent messages, e.g. InBox messages and emails.
The entire system is asynchronous and uses JMS heavily
Clients post messages via JMS
Messages are then routed via a routing service to the appropriate mailbox or directly for email processing
Message delivery: either Pull (clients request their messages), or Push (e.g., sending emails)
They use Spring, with proprietary LinkedIn Spring extensions. Use HTTP-RPC.