Sun Java System Messaging Server 6.3 Administration Guide

26.3.11 Slow Response After Users Press Send Email Button

If users are experiencing delays when they send messages, it may be because disk input/output is reduced due to insufficiently sized message queue disks. When users press the SEND button on their email client, the MTA will not fully accept receipt of the message until the message has been committed to the message queue. Information on message queue sizing can be found