1. to do it properly you need to have control over the reverse zone. that's a matter to check with your isp. (and do they really not have any reverse set up? some do, some don't)
2. you can do it yourself anyway with an entry similar to your 0.0.127.in-addr.arpa one, but it will only be valid for machines using your dns server to do reverse lookups. also add "notify no;"
3. alternatively, you should be able to send mail for your domains out through your isp's smtp server. but that's another issue.