e-mails get delayed in smtp queue

I am running exchange 2000 on a windows 2000 server. Recently my e-mail server started sending messages slowly. I noticed that messages are getting stuck in the PresubmissionQueue. It waits until there are 8 messages and then it sends them all. This only started happening about a month ago. E-mails used to go instantly and I never had anything sitting in the queue. What can I do to change it back to sending instantly?