A number of ISPs including Orange (previously Freeserve/Wanadoo) and AOL block access from your internet connection to any SMTP servers outside of their network in an attempt to reduce the amount of unsolicited mail being sent out of their network. This can be very inconvenient, especially for people on the move who use various ISPs and so need to be able to have a standard SMTP server such as that with your hosting account that can be accessed from anywhere.
Due to this restriction, we also have your SMTP server available on an additional 'port', namely port 587. You can normally alter the SMTP port within your mail client and change it from the default port 25 to the above port 587. This will then allow you to send mail again via our servers whilst using an ISP that would normally block this.
To change this setting in Outlook Express for example, from within Outlook Express click Tools -> Accounts -> Select your account -> Properties -> Advanced. You will then see the default setting of Port 25 in the 'Outgoing mail (SMTP)' section which you can subsequently alter.