When new users register, they automatically receive a welcome email. When the email verification box is checked under configuration settings, they also receive a verification email.
If these automatically generated letters are being sent but the body of the email is blank, check these settings:
1.) Go to:
Admin >> Edit >> Configuation Settings >> Path & URL Settings >> Mail Templates
2.) If you have installed in a standard manner, make sure that field is blank (FBB will default to the standard template setting).
3.) If you specified a path, be sure it is writeable and available. Also, make sure that the necessary files have been moved there. These include the relevant *_html.php and *_text.php files normally found in /templates/fusionbb/ directory.
4.) The actual content of the strings within these emails are found in /common.php in your language directory.