I have one user in my organization that has about 550 emails in her outbox for future delivery. What they are for - medical appointment reminders to others within the agency for our clients. She uses both Outlook on her "regular desktop" as well on the terminal server (Windows 2008). Outlook 2010 on both, using Exchange 2003 on Windows Server 2003. Sometimes, she will get a batch of emails "undeliverable" to staff that no longer have emails in the organization. When we have staff turnover (frequently) she has to go into the outbox and remove the staff that is no longer at the location/organization and put in the new staff. Sometimes, these emails will be from 1-2 months late in their undeliverable status or 1-2 weeks. The undeliverable message is just that she can't send to that person as they don't have an email. When she looks in her sent messages, it does not show that it was sent to that person, but the people it was supposed to go to. She is not using cached mode on either instance of Outlook. I don't know if it is an Exchange issue or an Outlook issue. She is the only person within the agency that has that many delayed delivery messages. Others may have one or two, most have none. I think she used to have cached mode on, but I turned it off so in case the message was sent and outlook happened to be closed for some reason.