You should tell us more about the process and the desired output in order to get more focused answers. Sounds like you don't really want to populate form textboxes. You want to get records from a table based on some value on a form, or you only want to get some of the fields from the records that are already on a form. How you would want to send that will make a difference because you can output table or query results in more than one format or method.
You might only need something as simple as a new query that only gets the fields you need based on a form or subform value, and then output that in an email.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.