I have a client who can no longer send emails. The set up they have consists of a server running Windows Server 2003 SBE and 7 clients with Windows XP SP3 installed. Recently they have a problem sending emails. This affects all of the clients who each use either Outlook Express, Outlook and Thunderbird. They can receive emails with no problem but they cannot send. Their email addresses are - email@example.com. I have checked with service provider and the person who manages their email and they assure me that there is no problem on their end. If they use a hotmail account there is no problem but their own business domain is not working. What should I be looking at to fix this problem?