Problema con SMTP

Hola Grupo,

Tengo un servidor de correo, el cual esta detras de un firewall. Este
servidor recibe los correos externos, chequea que no contengan spam o
virus y los "parsea" a mi servidor interno Exchange 2003. El servidor esta
unido a un dominio en windows 2003. El problema que tengo con este
servidor, es que cada 48 o 72 Hs, me comienza a dejar todos los correos en
Queue.
La solucion que encontre hasta ahora es reiniciar el servidor. Probe
sacando el servidor del dominio y volviendolo a unir, pero no paso nada.
Agradecere inmensamente cualquier aporte. De Antemano, Gracias.
Estos son los errores que arroja el Event Viewer:

Event Type: Error
Event Source: Userenv
Event Category: None
Event ID: 1000
Date: 14-11-2005
Time: 13:26:13
User: NT AUTHORITY\SYSTEM
Computer: MAILGATEWAY
Description:
Windows cannot determine the user or computer name. Return value (14).

For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.



Event Type: Error
Event Source: Userenv
Event Category: None
Event ID: 1000
Date: 14-11-2005
Time: 13:44:05
User: DOMAIN\username
Computer: MAILGATEWAY
Description:
Windows cannot establish a connection to domain.something.else with
(1311).

For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.



Event Type: Error
Event Source: Userenv
Event Category: None
Event ID: 1000
Date: 14-11-2005
Time: 13:44:05
User: DOMAIN\username
Computer: MAILGATEWAY
Description:
Windows cannot query for the list of Group Policy objects . A message that
describes the reason for this was previously logged by this policy engine.

For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.