This problem is permanent and happens to me ONLY when Outlook is closed.
I open Excel (or other product that have the capacity to send mails) and I type something in it, then I send this content by mail, to somebody.
From task manager I can see how Outlook "wakes up" and seems to catch the mail to send but it doesn't send. The message gets stuck in the "outbox", and it should not.
Only when I open Outlook manually, the message is sent immediately.
What is wrong here? Is it a configuration problem in my Outlook?