Outgoing mail lost in cyberspace

I am on the road and unable to test the computers with problems until next week but three experienced users of different computers (not connected in a network) in my company report the same problem: when using Outlook Express they do receive messages regularly but messages sent are "lost" in cyberspace and never reach the intended destination, although they do show up in "mail sent" as regularly sent, and no message alerting of any problem is received. The problem DOES NOT seem to involve the company managing the E-mail, Italy's largest (virgilio.it), because they are able to send mail via Webmail. The same company say they see nothing wrong with their E-mail and suggest this may be due to Norton's latest updates. Disabling and even disinstalling Norton did not solve the problem, however. Norton assistance claims a worm or Trojan may make this and I wonder whether this is a real possibility nad what to do. Two of these computers use Outlook Express and one the new Outlook, one has Norton 2004 with updates and one has Norton 2006.
Thanks for any assistance
Best
CESNUR

 

PS One of the employees found his computer is infected by ratorefaci\sysrtmvs.exe and other malware/spyware in the ratorefaci folder.
While these may be otherwise annoying, can this really cause the outgoing E-mail to disappear?
Best
CESNUR

 

Help in this tricky matter would really be appreciated
Best
CESNUR

 

Will do as soon as I return home in all three computers. This may be either next week or beginning of October so do not be surprised if you do not hear from me before

Best

CESNUR

 

Apparently, a national cat is out of the bag and has nothing to do with malware (perhaps). The story is this: Fastweb and Tin arethe two largest Italian high-speed ISPs. There are also political questions between the respective owners. Many users left Tin (a branch of Telecom, the largest Italian phone company) for the speedier Fastweb. We did and get weekly call fron Tin to return home. Apparently now a hidden part of this campaign is that Tin has found a way to block outgoing messages from their (paid for) accounts virgilio.it sent from computers connected to a Fastweb network.
Of course we have the outgoing mail correctly set with "server authentication needed" duly crossed.
Evidence that this claim by Fastweb is true is that the same laptop is able to send mail from a virgilio.it account when connected to a non-Fastweb LAN while when a Fastweb connection is used the mail is registered as sent but never reaches the intended destination. Vice versa, with a Fastweb connection mail sents from non-virgilio.it accounts duly reach the destination.
The question is legal and political but the problem is that while lawyers work virgilio.it users connected via Fastweb should either switch to another E-mail address (which Fastweb would even provide for free) or switch to another ISP (which Virgilio/Tin would compell us to do).
Question you may perhaps answer in your wisdom: how does Tin/Virgilio do it? and is there a way to trick Virgilio into NOT recognizing the mail sent by a virgilio.it account as coming through a Fastweb connection?
Hope the whole mess is clear
Best
CESNUR