A messaging server is software that handles and formats messages and messages so that they can be processed by messaging clients. The messaging server processes messages, stores them, and transfers them between two or more applications using a messaging API
(MAPI). Messages cached in the messaging server can be assigned priorities according to which they are processed.
A typical messaging server application is Microsoft's Exchange. The software resides on the messaging server and routes messages in the order they arrive. Depending on whether the messages need to be routed to local or remote receiving sites, this can be done immediately upon receipt of the message, or the messaging server can query other servers in the environment. If the messaging server cannot determine where to send the message, it sends a delay notice back to the originating server. This lets the userknow that the messaging server is having delivery problems and that it is trying to resolve them.