[MickDoneDee]

There is no setting. Currently it is unchecked which means you have to remember to check it before sending the PM, otherwise, the system won't tell you in Track Messages whether the PM was read.

The checking condition is controlled by the variable $checked[receipt] in the pm_newpm template. But I can't find the file that contains the variable to change its value. I looked in private.php and found the other PM options;

PHP Code:

        construct_checkboxes(array(
            'savecopy' => true,
            'parseurl' => true,
            'signature' => iif($vbulletin->userinfo['signature'] !== '', true) 


A template hack can have Request a read receipt for this message checked by default.
In the pm_newpm template replace $checked[receipt] with

checked="checked"