I have found that I am not always getting the results of my field lookup for email addresses in my form.
Use case: The user identifies themselves as the one who completed the form by selecting their name from the 'Completed By' drop down. This 'Completed By' drop down is populated from an HRExtract SQL table. When that selection has been made, a second lookup fills a hidden field with the user's email address which is from the same HRExtract table.
On some forms this email field gets filled and on others it does not. I have not been able to identify any other commonalities among those that do/do not show the email. I do have the hidden field set NOT to ignore the content when hidden.