We have noticed increased problems with some customers sending email.
One solution to this problem is to change your outgoing (SMTP) mail server to smtp.tein.net

Outlook Express & Outlook 2000/XP
Open Outlook Express, from the menu select TOOLS - ACCOUNTS, click the MAIL tab, select your mail account (usually mail.tein.net) and click PROPERTIES, click the SERVERS tab, in the box labeled "Outgoing Mail (SMTP)" change the server name to smtp.tein.net, click OK, then CLOSE. If you still get a message saying that it is unable to find the server you may neet to reboot your computer.