Received messages cannot be sent outbound for delivery. This means that they remain in the queue. Each received message is assigned as a mail object in memory. When the message is deposited in the Drop directory, it is removed from memory. If messages cannot be delivered, and you reach the default value of 100,000 objects, the system generates an "Out of Memory" error.

Check the following performance counters:

• Local queue length
  
  
• Remote queue length
  
  
• Local retry queue length
  
  
• Remote retry queue length
  
  

If the first two counters have values of 0, it indicates that messages are being delivered immediately upon receipt. If the value is larger, it indicates that there is a delay.

If the retry queues have high values, it indicates that messages cannot be delivered. Open the .rtr files to determine what is causing the problem.

For example, if a remote server is down, the remote retry queue length may have a high value and .rtr files in the Queue directory might include the error message "Host not found."