Outlook 2007 Postfix error 0x800CCC80

On many of my customers I've got a Fax Server made with Hylafax.

Faxes traffic is notified by email and because of this postfix is installed without too much security, the reason of this is that emails are sent only locally: no internet access for the Fax Server.

Well, today they introduced Outlook 2007 in one client and mails from that outlook 2007 client are not sent anymore with error 0x800CCC80.

How to fix this? After some checks I noticed