If you are using a database like MySQL, that doesn't support placeholders, your benchmark isn't really surprising as DBI emulating it is probably no faster than a simple string concatenation.

What might be faster, is using bind_columns to save yourself some copying:

    $sth->execute();
    $sth->bind_columns(\my $id, \my $subject, \my $body, 
                       \my $mailto, \my $mailfrom, \my $type);
                               
    while ($sth->fetch) {
        # loop as before
    }
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What I'm interested in, but haven't had time to play with is the new functionality added in DBI ver 1.30 (docs) for fetchall_arrayref:

$tbl_ary_ref = $sth->fetchall_arrayref( $slice, $max_rows );

If $max_rows is defined and greater than or equal to zero then it is used to limit the number of rows fetched before returning. fetchall_arrayref() can then be called again to fetch more rows. This is especially useful when you need the better performance of fetchall_arrayref() but don't have enough memory to fetch and return all the rows in one go.

Hope this helps...