How do I add a custom user field to emails

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Hi

I have added a custom user field which is a society registration number to the user and it appears on all tables etc however I would like to add the field to the notification emails but cannot find any information on how to do so. Any pointers would really help!

I have a similar question...

What would be the code to add to the HTML email version if we want to include a custom field from the product table? Would it be

<?php echo $data->product->XXX; ?>
where XXX is the column name of your custom field of the table "product" ?