This is Outlook Express 6 on Windows 2000. (I've tried everything I could find to solve this problem, including a complete uninstall and reinstall of OE6--on reinstall I restore the account and the problem is still there).
Here's the problem: When you send a message it goes to the Outbox, the message gets delivered, but it never leaves the Outbox and does not get put into the Sent folder. This only happens with POP3. If I set the account to IMAP, everything works okay. But it needs to be set as POP3.