Two steps are needed in order to correctly apply back-pressure in an Akka system: Step 1: Bounded Mailboxes and Push Timeouts The default mailbox for an actor is an UnboundedMailbox backed by Java’s ConcurrentLinkedQueue. As the name indicates, this mailbox grows without bound and will end up crashing the JVM with an OutOfMemoryError if the consumer significantly slower than the producer. If we wa