I assume that you do not have spaces in your e-mail address CSV, otherwise this would be the first thing to do "regsub -all { } $email {} email".
Furthermore make absolutely sure that there is no blank line or anything like this in your CSV file at the end.
And last but not least, think about getting rid of the db_transaction and just log (instead of stop) on error, so you know which users failed to get inserted.
