Write Perl not C (see the for loop below). Use strictures and lexical variables. Use early exits (that's yes use next to your question btw). Oh, and use place holders in your SQL:

for my $datum (@{$mydata}) {
    my $account_number = $datum->{'account_number'} || '';
    my $name           = $datum->{'name'}           || '';
    my $email = $datum->{'email'};

    if (! $email) {
        bad_email("No email address found '$account_number'.");
        next;
    }

    if ($email !~ /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i) {
        bad_email(
            "Invalid email address - '$email' on account '$account_num
+ber'.");
        next;
    }

    next if ($name eq '') || ($account_number eq '');

    # Send  emails
    send_email("send my stuff here");
    my $data = qq(<tr><td align="left">$account_number</td><td>$email<
+/td></tr>);

    push @all_data, $data;

    my $sql = "update table set date = ? where number = ? and date = ?
+";
    exec_single_sql($sql, $db, $datetime, $account_number, $datum->{da
+te}) 
        or die "Unable to update table";
}
[download]