Although the $bulk->LIST() can effectively accept a code-reference as a parameter, it won't work well in this context. To extend the previous comment, I would re-factor to the following logic, avoiding the code-ref and replacing with an array ref:

...

$bulk->LIST( $dbh->fetchall_arrayref() );
$dbh->rollback();   # Not necessary, but I like to do it
$dbh->disconnect(); # Look below for more detail

...
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Technically, DBI will automatically rollback and disconnect via the DESTROY method, however there are the potential for warnings if you let DBI handle it, so it's always nice to do it your self.

Overall, this should not only fix your problem, but it shoudl also set the entire list of e-mail addresses in your database to the LIST attribute.