Outlook XP/2003 problem with 2 to 3 recipients

[Kainan]

I've had this problem with Outlook on one other computer and the only thing that fixed it was uninstalling and installing Outlook again. It was Outlook 2003 though and this PC is Office XP. Anyway, it is the strangest thing to me. We don't use an exchange server but I do have a 2003 server set up for DNS, DHCP, File sharing, etc. For some reason these two computers have had situations where they send emails through outlook to a list of people yet there are 1 to 3 recipients who don't get them. I've tested and the email leaves Outlook as if it is going but it doesn't make it to the ISP's Mail Server. I can send using the same account AT the mail server and it will go to all email addresses. I've also used the account info and sent an email to the problem addresses via another PC with Outlook and it works. So it is a problem contained on the machine sending from Outlook. It isn't those receiving or the Mail Server. I reloaded Outlook on the XP machine and no dice. They still can't get email to the problem recipients. One other thing is that those who can't receive from them are internal (same domain). If anyone has a CLUE as to why this would happen I would appreciat the input. Thanks in advance.