Open “Add or remove programs” wizard either from control panel or by running appwiz.cpl from Run window. Click on ‘Set program access and defaults‘ from the list displayed on the left. You will see the list of configurations available(Computer Manufacturer, Microsoft, Non-Microsoft, Custom). Select Custom from the list. Under the section ‘Choose a default e-mail program’ , you can see a list of email programs.
An alternative way to do this is to open the email application and change the settings. The exact operation varies based on which email application you want to set as the default one. For example, to set Outlook as the default email client do the following steps.
Open Outlook application
Select Tools -> Options
Select ‘Other’ tab
Then select the radio button “Make Outlook the default program for E-mail, contacts and Calendar”.