One way is to use bind_col or bind_columns:

$sth->execute($id) or err_trap;
$sth->bind_col(1, \my $e_mail);

while ($sth->fetch) {
  print "$e_mail\n";
}
[download]

Or without bind_col:

while (my ($e_mail) = $sth->fetchrow_array) {
  ...
[download]

Also, I notice you're checking for errors on the execute, but not on the prepare. That's a sign that you may be missing something, and maybe should consider using RaiseError (see the DBI docs) and maybe HandleError also.