This is a fairly broad problem and can be the result of several factors. Please go through this list and eliminate each possible cause:

• Make sure you have your outgoing SMTP Mail Server set to mail.yourdomain.com.
  
• Make sure you have a connection to the Internet when trying to send outgoing mail.
  
• Make sure your domain name is pointing at our name servers.
  
• Make sure you have first checked for new e-mail before sending outgoing mail.
  
• Make sure that all recipients have a valid e-mail address.
  
• Make sure that your Local Area Network or Internet Service Provider are not blocking access to port 25. You can try port 26 to see if they are not blocking it as well.

If all these requirements are met, there should be no other reason that you cannot send outgoing e-mail through your SMTP server. The most common problem is that a client will forget that they must first check for new e-mail before attempting to send. Additionally, new clients usually have this problem while their domain name is in the process of propagating or is in the process of being transferred to Workingdogs or Dogbits, in which case they must simply wait for propagation to take place.