I have a few computers with Outlook 2010 configured to work with the IMAP server. On the all of them in the account options I've set it to store sent items in the sent folder on the IMAP server. The problem is it works but only sometimes (randomly) for some e-mails. When the sent items aren't stored on the server then they are stored locally in the user's mailbox sent. This is strange behavior and I don't see any logical pattern it fallows.