If Thunderbird is your email program, when you send email directly from FileMaker, it should open up Thunderbird with the target email address already filled in.
However, after doing a Windows Update, the default email program can be changed to Microsoft Outlook, and then the direct email from FileMaker no longer works.
To fix this problem in Windows XP, open up the Control Panel, and select Internet Options.
Double-click on Internet Properties which should open the following window. Select the “Programs” tab.
Change the selection next to E-mail to “Mozilla Thunderbird” as shown. Click on the OK button to save the change.
You should now be able to send email directly to Thunderbird from FileMaker.