There are two Message Exchange Patterns you can use in messaging.
From there Enterprise Integration Patterns they are:
Event Message (or one-way)
In Camel we have an
org.apache.camel.ExchangePattern enumeration which can be configured on the exchangePattern property on the Message Exchange indicating if a message exchange is a one way Event Message (InOnly) or a Request Reply message exchange (InOut).
For example to override the default pattern on a JMS endpoint you could use the
exchangePattern parameter in the Endpoint URI as shown: