Due to improvements with our email system preventing spam from the 23rd July 2010, we need to advise you that if you are unable to send email, you will need to change the port from 25 to 587.
In short:If you have no rDNS set up on your ISP, you might not be able to send any email, therefore need to use port 587 with authentication, instead of port 25;Since this change, port 587 is for users to send out emails on. Port 25 is for servers to relay messages to one another. That way ISPs can block outgoing SMTP on their networks but still allow users to send email to any mail server through port 587.
Furthermore, we have a system in place that whenever failed login attempts are logged, the IP will be blocked for 24 hours.