Normally there is no need to make an email client as default email client for sending or receiving email. It's mainly useful to allow other applications to use for example, when you click on a mailto: link or when you click File -Send link in Firefox, you can set for example Thunderbird to open.

Of course you can manually configure an email client being default, but in Windows XP there is no option to set a per-user default email client. One setting affects all the users, machine-wide.

And also for an average user manually setting an email client (example Thunderbird) to default client is normally difficult.

DefaultMail client utility helps you set the default email client for the currently logged on user account in Windows XP quite easily.

Just download the tiny tool (21Kb), unzip and run it. Select a mail client from the list that you want to set as default and click Apply to confirm the settings.

Download the free tool from the program’s home page. More information here