Problem sending e-mails automatically

Dear folks, maybe I posted this before months ago. This is not exactly a post about Navision, because there are serveral factors. I've the following code:

IF "Salesperson code" = 'person' THEN BEGIN
CodeMail.NewMessage('mail@mail.com','','This is a testing' + "Item",
'','',FALSE);
END;

CodeMail is the codeunit Mail.

I put this code (and others changing the e-mail and sales person) on Onvalidate trigger in a table field. When anyone write in this field automatically sends an e-mail to the address according to the sales person code. It works fine, but only in some computers, in other computers don't send any e-mail, simply doesn't do nothing. I've come to the conclusion that is problem of Office or Outlook configuration, because the code runs well. All the computers have the same version of Navision (3.70), the same O.S.(WXPProf. SP2) anda the same version of Office (2003), this is the reason because I don't know what can be the problem. Does anybody knows what happend? Have you had a similar problem?.
Thanks in advance.