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Reverse DNS | BT Business

Reverse DNS

Reverse DNS (or rDNS) is a change to your IP address which helps to prevent your email being marked as spam. This is widely used by businesses who have set up their own mail server, or who often send out mailing lists to their customer base.

How does it work?

Reverse DNS works by changing the "Host Name" on your static IP address to your fully qualified domain name.

This means that when firewalls and other security measures can match your IP with your domain email address to double check that you are who you say you are, and that your email is from you and not a spammer pretending to be you.

For example:

If my email address is 213.x.x.x and my mail server is
My Reverse DNS would link the two.

If I send an email from 213.x.x.x the receiver's computer would look up the rDNS match this with and be more likely to allow an email from a email address.

Setting up a reverse DNS on your domain name

If you're using one of our static IP addresses, we can setup custom rDNS setup (at our discretion) for no additional cost. To set this up please contact us using our reverse DNS form providing the following information:

  • Your BT provided static IP address you wish to use (e.g. 213.x.x.x). This is usually the static IP address you've assigned to your mail server. We can do this for up to 8 static IP address. If you require more, we'll need you to provide a technical justification for each rDNS record.
  • The domain or sub-domain you use for your mail server (for example Please note we may require proof you own the domain before we can setup the rDNS entry.

We'll usually process your request within 7 days and email you to confirm it's been done.

Change or remove the reverse DNS on your domain name

If you have your own local mail server, you might encounter problems sending emails through some spam filtering systems because of security processes known as reverse DNS lookup (rDNS).

If you’ve set up custom reverse DNS with BT but want to change or remove it please use our Reverse DNS form.

You'll need to include the following information when you fill in the form:

  • Broadband number - If you aren't sure what your number is, plug a telephone into the socket and dial a mobile number which should then display your broadband number (if it's withheld then dial 1470 before the mobile number).
  • Broadband Account number - This is the account that your static IP number is on.
  • Fully Qualified domain name. - These could be displayed as or
    Non fully qualified domain names could be displayed as or example.local.
  • IP Address that you want to change/remove.

We’ll reset your rDNS to the default settings unless you provide any special instructions.

Requests are processed manually and are usually completed within two working days, but delays might occur during periods of heavy demand.

A confirmation email will be sent once the form has been received. When the changes have been processed another email will be sent to confirm the changes to your rDNS.

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