ENUM Domain – What Is It?

ENUM is derived from the term telephone number mapping. ENUM domains make Internet and telecommunication services available under a single telephone number. Under a single ENUM domain, a person's business and home phone, mobile phone, fax, business and private e-mail addresses, video conference addresses or websites may be addressed. The application that is being used at a given moment to get into contact with someone identifies the destination address that corresponds to the ENUM domain. Thus, ENUM automatically ensures that the message is sent to the appropriate device.


  • E-mail program: e-mail address
  • Telephone call: fixed-line phone, mobile phone or IP phone

ENUM Domain – How Does it Work?

ENUM makes use of the Domain Name System (DNS). The linking of telecommunication resources and the Internet is achieved by registering an ENUM domain for a telephone number. For example: The telephone number +49 12345678 is assigned to the ENUM domain, including the domain holder's various communication services.

Since 2006, ENUM domains of the German number space have been registered by DENIC. The ENUM domains administered by DENIC under the German country code +49 are under 9.4.e164.arpa.

An ENUM domain for a particular telephone number can only be registered by the person holding that number. For ENUM domain registrations, DENIC's ENUM Domain Terms and Conditions and ENUM Guidelines apply. In order to ensure that an ENUM domain is actually registered by the legitimate holder of the corresponding telephone number, DENIC provides a Complaint Procedure.

Register and Update an ENUM Domain

If you wish to register an ENUM domain, please proceed as follows:

Step 1: Registration

Request a provider who offers ENUM domains to handle your registration (List of ENUM Members). 

The name service, through which the communication entries are determined, may either be requested from a DENIC member or any other provider, or you can do this job yourself.

Registration as an ENUM domain is only possible for those domains that correspond to geographic telephone numbers (all numbers with German area dialling codes), mobile numbers within the (0)15, (0)16 and (0)17 ranges, national numbers ((0)32), national free phone (toll-free) numbers ((0)800), personal telephone numbers ((0)700) or service numbers ((0)18).

Before you place your domain registration request, you should be familiar with the ENUM Domain Guidelines. These contain the rules that apply for ENUM domains under 9.4.e164.arpa. A domain contract with DENIC can only be concluded if all the conditions laid down there have been fulfilled.

The provisions applicable to the domain contract are summarised in the ENUM Domain Terms and Conditions. These describe and explain the rights and obligations of domain holders and DENIC.

Step 2: Correct User Data

In order to register an ENUM domain, you must be the legitimate user of the corresponding E.164 telephone number. You have to provide accurate and complete data.

Inform your provider without delay of any changes to your domain data or in case you cease to be the legitimate holder of the telephone number. With the registration of the domain, you have undertaken to keep your domain data always correct and up to date. Inaccurate data entitles DENIC to terminate the domain registration contract. The correctness of your data is validated at regular intervals.

If the annual revalidation procedure reveals that your data is not up to date, the ENUM domain registration will not be renewed and the domain will be deleted.

Updating the Data of an ENUM Domain

We only accept UPDATE requests for domain or personal data from the DENIC member administering the ENUM domain at the time.

Carry out a Provider Transfer for an ENUM Domain

Changing providers for an ENUM domain is possible at any time. Please keep in mind that the one-year registration period of your ENUM domain will restart after a provider transfer.

Our standardised Provider Transfer Procedure ensures that your ENUM domain remains registered without interruption.

To change providers for your ENUM domain, proceed as follows:

Step 1: Contact Current and Future Provider

To change providers, please contact your current provider directly. Tell your new provider to take charge of administering the domain.

Step 2: Validation and Request

The new provider will check that the requested provider transfer has really been initiated by you as the domain holder or your legal representative and not by any third party. The new provider will also verify that the domain holder is the legitimate holder of the corresponding telephone number (Validation). Subsequently, your new provider will submit the formal request for a provider transfer to DENIC.

Step 3: Processing of the Request

DENIC sends your provider transfer request for confirmation to the member currently administering your ENUM domain. This member will also check whether it has received a corresponding notification by you. If so, the DENIC member will return your acknowledgement to DENIC. If not, the member will return your rejection to DENIC.

If DENIC does not receive an answer within three working days, we send a reminder to the DENIC member who is still in charge of the domain. If there is no reaction to this reminder, DENIC takes this as confirmation that the member who has been in charge so far recognises the check by the future provider as correct.

The provider transfer will then be carried out and the data entries will be updated. At present, the provider transfer is usually completed after five days at the latest.

Factors That May Lead to Delays

If there is any doubt, the member or provider will reject the transfer, so as to prevent misunderstandings or even misuse. The provider will try to contact you to seek clarification. This may become necessary if:

  • You have given notice to your provider, but the provider has not yet informed the responsible DENIC member.
  • You have forgotten to give notice of termination.
  • The DENIC member has been unable to contact you.

Once things have finally been cleared up, the DENIC member can still acknowledge the transfer that has been rejected initially. The data of the member in charge will then be updated immediately.

Accessibility of ENUM Domains During a Provider Transfer

Whether or not your ENUM domain is accessible during an ongoing provider transfer procedure does not depend on DENIC, but on the arrangements that you, as the domain holder, have made with your providers (both the old one and the new one).

If your old provider ceases to provide the services before the new one starts to provide them, using the domain might not be possible, though it remains continuously registered in your name.

Renew the Registration of an ENUM Domain

ENUM domains are registered for an initial period of one year only.

If you wish to go on using your ENUM domain, you must request the renewal of the domain. For this purpose, you will be required to submit evidence that you are still the legitimate holder of the corresponding telephone number.

Usually, your provider will contact you in good time before your ENUM domain expires and will then perform revalidation and renewal on your behalf.

Validate an ENUM Domain

Background Information:

We must be sure that an ENUM domain can only be registered by the person who is actually authorised to use it. For this reason, every DENIC member is obliged to check this authorisation before accepting any request for registration, renewal or provider transfer.

DENIC members can apply their own methods for validation or make use of a validation service provider. In either case, DENIC members must make sure that they are in possession of a positive validation for each ENUM domain. The validation must not be older than twelve months. If required, the member must submit the validation information to DENIC.

To ensure a high degree of data integrity, contracts for registration of an ENUM domain are not unlimited, but are always made for one year. In case of positive revalidation, a contract may be extended for a further twelve months.

Delete an ENUM Domain

If you want to delete your ENUM domain, please contact your provider. Make sure to tell your provider clearly that you want to completely give up and delete your ENUM domain. Most providers ask their customers to use special forms for a deletion request.

DENIC will only accept deletion requests submitted by the DENIC member who is, at the time of such request, in charge of the ENUM domain in question.

Please note: Once a deletion has been carried out by DENIC, the corresponding domain cannot be restored without the involvement of a provider. If you want to go on using an ENUM domain, you have to request a provider to register the deleted domain again with DENIC.

ENUM Complaint Procedure

In case of doubt with regard to the legitimate holder of a telephone number, our ENUM Domain Terms and Conditions entitle DENIC to disconnect the ENUM domain. However, before this happens, we will always try to clarify the situation, consulting all parties involved.

Complaints about supposedly wrong ENUM domain delegations can be submitted to DENIC by e-mail, fax or letter.

The case will then be clarified, step by step, within a clearly defined time framework. DENIC and the provider responsible for the domain will do everything to enable ENUM COMPLAINTS to be clarified as quickly as possible. Upon presentation of the correct data, they may arrange for the domain to be delegated newly if required.

If it can be proven that the ENUM delegation was wrong, DENIC will have the right to terminate the Domain Contract without notice.  Furthermore, we will keep records of such cases.

Parties Entitled to File ENUM COMPLAINTS

The ENUM COMPLAINT procedure may be started by:

  • DENIC members
  • The network operator of the telephone number
  • Legitimate holders of an E.164 telephone number
  • Someone else acting on behalf of the legitimate holder, submitting corresponding proof
  • Third parties (in justified cases)

Workflow of an ENUM COMPLAINT:

Step 1:

One of the parties entitled to do so initiates the COMPLAINT procedure. The legitimate holder of the E.164 number is required to identify themselves before submitting a complaint and also to submit proof to DENIC that they really are the legitimate holder of the number concerned. A DENIC member acting on behalf of the legitimate holder must validate the holder's legitimacy or demand evidence of such validation. The network operator, too, has the right to initiate the ENUM COMPLAINT procedure with DENIC once the validation information is available.

Step 2:

DENIC checks the evidence submitted regarding the right to use the telephone number and, if necessary, requests further documentation from the ENUM domain holder and the DENIC member in charge, or the holder's provider.

Step 3:

After checking the evidence and information obtained, DENIC decides whether the request to delete the ENUM domain will be executed or rejected. All parties involved will be informed of this decision. If the request is executed, DENIC will terminate the existing registration contract without notice. The ENUM domain may then be re-registered.

Technical Specification

The ENUM specification was developed and managed by the IETF in the ENUM Working Group, which had been established for this purpose:

RFC Published Status

RFC 2916
RFC 3761
RFC 6116

September 2000
April 2004
March 2011

valid version

RFC 6117

March 2011

valid version

RFC 6118

March 2011

valid version

RFC 6116 describes the basic technology of mapping telephone numbers (E.164) to the Domain Name System.
RFC 6117 defines the requirements for the specification of new ENUM services.
RFC 6118 revises all ENUM services defined under former RFCs.

For a comprehensive overview of all RFCs, please refer to the RFC Archives of IETF or to the RFC Editor website.

Technical Background Information

The ENUM protocol was developed by the ENUM Working Group of the IETF (Internet Engineering Task Force) and documented in the Internet standard RFC3761. There are some other Internet standards for future RFCs in this field. Access to the ENUM services on the Internet's existing Domain Name System (DNS) is via a subdomain reserved for ENUM. The IAB (Internet Architecture Board ) proposed .e164.arpa for this purpose, since E.164 is the standard in which the ITU (International Telecommunications Union) describes the international telecommunications number plan and .arpa is a specific Top Level Domain used as "Address and Routing Parameter Area" for infrastructure services. It is RIPE NCC in Amsterdam that acts as the international registry for .e164.arpa. Under this subdomain, an ENUM domain is then formed according to the following rule: the digits from the telephone number are placed before the .e164.arpa ending in reverse order and separated from one another by dots. To give an example, DENIC's telephone number is +49 69 27 2350 and it is linked to the domain

As far as the German part of the ENUM name tree is concerned (i.e. .9.4.e164.arpa), it was agreed with the relevant decision-making bodies to delegate it to DENIC. The lower levels can then be administered by the providers or by the customers themselves.

Requesting an ENUM

Technically, an ENUM request functions like this: once the user has entered the desired call number, the ENUM client accesses the so-called Naming Authority Pointer (NAPTR) records via the .e164.arpa name server on the ENUM name server. These records contain information about the available services that are combined with a particular E.164 call number. The result of this ENUM request may be just one or several URIs (uniform resource identifier), including the sequence in which they are to be processed. These URIs are now used to address resources or services that are associated with the E.164 call number.

ENUM Domain Request

[Translate to English:] ENUM Domainabfrage
  1. Input of the fax number (+49 1234) of the subscriber at the sending device.

  2. Request of the sending device to the ENUM DNS server using the ENUM domain ( of the dialled number.

  3. Answer of the ENUM DNS server delivers a list of possible communication items, among them the information to which URL (ifax:fax@denic.de) an incoming fax message has to be sent.

  4. Establishing a connection via the Internet between the sending and the receiving fax device.