Ok, time for some tech speak! Many ISPs are blocking the outbound SMTP port 25. It allows ISPs to block spam sent out through their networks, but it tends to “punish” those who innocently need to send stuff through e-mail servers, rather than those belonging to their ISP.
In a nutshell, here are some of the possible scenarios that you might encounter when using port 25:
1. Sending an email from your Outlook Express or Outlook (assuming you’ve configured the email client to use the default port 25 for your SMTP server)
2. Submitting a web form (assuming the back-end was done using a SMTP method)
3. Using Groupmail to deliver email newsletter (assuming the Groupmail is configured to use port 25)
In short, your emails will be blocked and the worst thing is, they’re usually dropped without any returned error messages or notices to the sender. To overcome this issue, we’ve setup an alternate port. You can use port 8025 or port 587 instead of port 25.