A message server is an application that handles messages between two or more applications. These messages are passed to the middleware application using a messaging API (MAPI). Messaging servers can store messages in a queue until they can be delivered to recipient applications.
Server racks.
A typical example of a mail server application in many organizations is Microsoft Exchange. Exchange sits on a server and waits for messages to be routed to its queue. From there, the middleware determines one message at a time whether the message should be routed locally or sent to another messaging server for delivery. If the message belongs to a local recipient, it will be delivered to the local mailbox almost immediately. If the message belongs to a remote message store, the Exchange server will query other application servers in a DNS-like environment to find the server that the message belongs to.
If there are connectivity problems between two messaging servers, or if the sending server cannot determine the location of the remote server, the person sending the message may receive a delayed delivery message from their server. Typically, this message will let the person know that the server is experiencing difficulties, but will keep trying for a specified number of attempts or days.
There are other types of message servers or email servers. Some, like Qmail, run on the Linux operating system and require much less overhead and administration than an Exchange server. This makes them ideal for ISPs that host a large number of customer email accounts. Many businesses use Microsoft Exchange for messaging because it is very reliable and works well with other Microsoft products used by businesses.
When a person sends a message, Outlook (or your messaging client) passes the message to the messaging server, where the message enters the message queue to await its turn to be processed. If there are a lot of messages going through the queue, this process can take a while, although normally no one will notice the transition. When the message is processed, the messaging server determines the location of the recipient’s mailbox. If the mailbox is local to that server, the message will be delivered immediately to its destination. If the recipient is not local to the server, DNS will be contacted to help locate the server on the Internet. When the server is found, the sent email message is transferred to the recipient’s server, where processing begins locally from a queue to handle the message. Once the correct mailbox is found,
