The error Outgoing mail blocked on port 25 occurs due to the misconfiguration of your ISP settings. The outgoing port 25 is usually blocked to prevent viruses and spams over your network. To fix this issue on Microsoft Outlook 2007, follow the below-mentioned steps.
Your ISP might block you from connecting to your mail server. However, it may also be caused by your local router or cable modem. To check if your router has blocked the SMTP port 25, follow these steps.