Internet Service Providers (ISPs) commonly place a block for outbound email traffic to servers outside of their control. They do this by blocking the default port access for outbound mail servers, which is port 25. In some cases, you maybe need to make a modification to your email client to get around this block. We have opened an alternate port, 8889, to accommodate this, which ISPs have been deploying to protect outbound spam from their networks.
For additional information, you may also want to see our article on how to use the alternate SMTP port in Outlook and Outlook Express
Article ID: 9, Created On: 3/18/2011, Modified: 3/18/2011