Sometimes it's possible for Outlook to get stuck downloading an email, to unblock it do the following:
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http://www.profesionalhosting.com/soporte/panel-de-clientes.html
2. Look for Horde Webmail.
3. Enter the data for the email account that is having the problem.
4. Click on "entrada" or "inbox". Look for the latest undownloaded emails by date.
5. Select it and click on "eliminar" or "delete".
6. Finally, click on "vaciar papelera" or "empty trash".
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If the queue is still stuck, repeat the process until your queue is cleared.