Reverse DNS that resolves
before your mail bounces.
The very first thing a receiving mail server wants to know has nothing to do with the content of your message. It wants to know whether your IP address has a PTR record, and whether the name in that record points back to the same address. If the answer is no, a good number of providers will simply refuse the connection before a single byte of the actual message has been read. The Prefixx portal lets you manage reverse DNS for your ranges directly. You can work one record at a time, import hundreds of records in one go, or hand entire zones over to your own nameservers, whichever suits the way you work.
Two ways to run rDNS. Both in the portal.
Managed records are what most of our clients use, so we will describe those first. You pick a range, enter an IP address and a hostname, and the portal writes the PTR record straight onto Prefixx's authoritative nameservers. Invalid hostnames are rejected at the point of entry, synchronization takes place without any further action on your part, and every record shows its status in the list as active, pending or failed. Records can of course be edited or deleted again later, whenever the need arises. And if you happen to be provisioning hundreds of hosts at once, there is no need to type them in one by one: the bulk import accepts a pasted list of IP hostname lines and reports any problems line by line. Anyone who has been through a midnight migration will appreciate the difference between correcting three rows and starting the whole batch over from the beginning.
Zone delegation is the second option. If you already operate your own DNS infrastructure, you may well prefer to run the reverse zone there too, and the portal accommodates this. You provide between one and four nameserver IPs for any range of /24 or larger. Prefixx remains the authoritative nameserver on record with the RIR, pulls the zone from your masters over zone transfer (AXFR), and otherwise stays out of your way. From that point on the PTR records live in your own infrastructure, where you can manage them with whatever tooling you are used to. Every delegation request is reviewed by a Prefixx administrator before it takes effect, and a pending request can still be cancelled if you change your mind in the meantime.
Ranges smaller than a /24 are a special case, and one that deserves a short explanation. Classic in-addr.arpa delegation does not work below the /24 boundary. The official workaround for this, RFC 2317 with its CNAME construction, has a reputation for being fragile and awkward to maintain, and in our opinion that reputation is well deserved. We therefore chose not to support it at all. Per-record management covers sub-/24 assignments completely, and you never have to operate the zone yourself.
From bare IPs to resolving PTRs.
Everything described below can be found under the Reverse DNS section of the portal.
Pick the range
The first step is simply to select an rDNS-enabled range, and that is genuinely all there is to it. The record list then shows you every PTR record that currently exists for the range, including the hostname and the synchronization status of each one.
Add records
Enter an IP address from the range together with the hostname that it should carry. Alternatively, you can paste an entire list in IP hostname form and let the bulk import work its way through it for you. Addresses that fall outside the range are rejected, and so are duplicates, and any errors are reported per line rather than as one unhelpful message covering the whole batch.
Confirm sync
At this stage there is nothing further for you to do. The records are pushed out to Prefixx's authoritative DNS on their own and change to active once they are live. Edits and deletions follow exactly the same path, and the status column will keep you informed the whole way along.
Delegate if you prefer
Should you prefer to host the zone on your own servers, go to the Delegations page, pick a range of /24 or larger, enter up to four master nameserver IPs and submit the request. There is one detail here that people forget time and time again: your servers must allow zone transfers (AXFR) from Prefixx's nameservers, because without that permission in place the delegation simply cannot complete. Once an administrator has approved the request, the zone is in your hands.
The first thing a mail server checks.
Every receiving mail server runs one particular test before it does anything else, namely forward-confirmed reverse DNS, usually abbreviated to FCrDNS. The IP address must have a PTR record, and the hostname in that record must resolve back to the very same IP address. If either half of the test fails, the large providers will greylist your mail or refuse the connection outright. And the importance of reverse DNS does not stop at mail, either. Abuse desks, security auditors and cloud BYOIP reviewers all tend to read missing or generic rDNS in much the same way, as address space that nobody is actively operating. Well-maintained PTR records show the world that your network is genuinely being run by someone. Since it is, there is really no reason not to let that show.
Or let us set it up for you
rDNS management is included with every client account. Clients on our white-glove service can hand the whole subject over to us: our team plans the PTR naming scheme, enters the records, sets up the delegation to your infrastructure where that is wanted, and verifies FCrDNS from end to end. You never have to touch a zone file yourself.
White-glove details →Reverse DNS: common questions
Not by delegation, no. Reverse zones align to /24 boundaries in in-addr.arpa, which means that delegating anything smaller would require the RFC 2317 CNAME workaround, and that workaround is fragile, fiddly, and rarely worth the trouble that it brings along with it. This is precisely why the portal offers per-record PTR management at any range size instead. It gives you the same degree of control, and there is no zone that needs looking after.
Your servers act as the primary (master) for the reverse zone, while Prefixx remains the authoritative nameserver on record with the RIR and pulls a copy of the zone over zone transfer. The one hard requirement is therefore that your servers permit AXFR from Prefixx's nameserver IPs. You can list between one and four master IPs per delegation, and each request is reviewed and approved by a Prefixx administrator before it goes live.
There is no waiting period on our side, if that is what you are asking. When you create, edit or delete a record, it synchronizes on its own while the status column keeps you informed of its progress, and a status of active means that the record is live. From that moment on, fresh lookups resolve immediately. The only delay anyone might still notice comes from their own resolver holding on to a cached TTL from the previous value.
Give every IP a name that answers back.
PTR management, bulk import and zone delegation are all included free of charge for Prefixx clients.
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