<?php
$o1 = new StdClass;
$o1->{"abc@gmail.com"} = array();
$o2 = new StdClass;
$o2->{"xyz@gmail.com"} = array();
$inDatabase = [$o1, $o2];

print_r($inDatabase);
      
$innerKeys =[];

for($i=0;$i<2;$i++){
    $temp = array_keys(get_object_vars($inDatabase[$i]));
    //so I thought $temp[0] would have the email address but $temp is null.
    array_push($innerKeys,$temp[0]);
}
print_r($innerKeys);
?>