If you disable «open» registrations and would like to force user to validate his email upon registering, you must uncomment and set the option
$closeRegister=1;in setup_options.php file.
However, if you're worrying about your members, it would be useful to provide some kind of additional information about that. For example, user doesn't see the «Password» link while registering, because the password will be generated/emailed to his email address; so you need some way to inform the user about that. The same way you should inform the user, that if he changes the password in Preferences, it will be also re-generated and resent to his email address, and his account will be blocked until he confirms it. After registration, user should also get a proper message about password has been sent and the registration is completed.
Below are minimal steps to fix your forums when this setting is up:
1) Paste in bb_plugins.php the following code:
/* email registrations addon */
if($action=='registernew' or $action=='register'){
$emailTitle='<br />Please, specify a valid working email address. Your forums password will be emailed there.';
}
elseif($action=='prefs' or $action=='editprefs') {
$emailTitle='<br />If you change your email address, a confirmation link will be sent on it. Until you confirm it, you will not be able to enter forums as a member.';
}
/* --email registrations addon */
2) Paste the variable
{$emailTitle} in templates/user_dataform.htm
l beneath the email field. For example that way:
<tr>
<td class="caption4" style="text-align:right">* <b>{$l_email}</b></td>
<td class="caption5"><input type="text" name="email" maxlength="50" size="20" value="{$email}" class="textForm" style="width:200px;" /><span class="txtSm">{$emailTitle}</span></td>
</tr>
3) Modify your language pack and change variable $l_goToLogin (it will be displayed AFTER user registers):
$l_goToLogin='Your password has been sent on the email address specified. Please, check it within the next few minutes. Only after validating your email and password, you will be able to sign in on forums.';
4) Starting from miniBB v3.5, email template for registration is no longer providing straight username and password visible. Replace this template to the alternative version, providing this data (unpack to the /templates/ folder an modify if needed).