When you are first exposed to the EasyLink Messaging API, there are a number of terms used that may be confusing.  This document explains some of these terms and how they relate to the API.


A domain is a complete system that processes and delivers messages.  Domains are independent of each other, with each having its own set of processing components, delivery agents, documents, and jobs.  When a job is submitted via the API, the domain name associated with that job is returned in the job submit response as the “MDN” portion of the JobId. 

Switch Type/Domain Type

Even though most of the processing components are the same, each domain is configured to deliver certain types of items.  The switch type is an indicator of which things are delivered by that domain. 

Switch Type is used in the API to indicate which type of domain to reach out to for certain activities where data is split between types of domains.  Examples are address blocking, list management, and stored object management.  For these functions, the request specifies the switch type, and the API figures out which specific domain to reach out to for the user.

The switch types are:

XDDS XDDS domains primarily deliver fax and voice messages, although there is some support for email and SMS delivery as well. 

MR (messageREACH) domains deliver Enhanced Email and SMS.

The API chooses the domain for job submission based on the elements specified in the <JobOptions> element, as follows:

Test and Production Domains

There are multiple different sets of domains available, depending on the phase of development of the customer's application. These sets are distinct from each other, with independent sets of user ID's, profiles, lists, objects, etc.  These different sets are:


The test domains are used for initial deployment of EasyLink software, as well as for testing of some client applications.  The specific domain names are test2 (XDDS) and flusme (MR).  User ID's created in these domains are often created with a prefix of "T2/".

Software installed in the test domains is often newer than what is installed in production.  We recommend that customers verify their production applications against the test systems when new software is installed there.


The production domains are for applications in full production mode with real traffic.  There are multiple domains of each type, and generally more than one of each type is associated with each user account, depending on their disaster recovery and business continuity requirements.

The following are the current production domains:

Domain Name

Switch Type




Primary domain for US users, as well as for most Fax2Mail users worldwide.



Secondary domain for most US and Fax2Mail users



Located in Europe; used for a limited subset of customers



Legacy domain in Europe that is being phased out in favor of xsi2



For Japanese users (other than Fax2Mail – Japanese Fax2Mail processes in xsi).



Primary MessageREACH domain worldwide.



Secondary MessageREACH domain configured for a subset of customers.

User ID's in production domains do not have specific prefixes, although they are sometimes prefixed with an indicator of the user's home country ("XSI/", "AU/", "UK/", etc.)

API Instances and URL's

There are multiple instances of the Messaging API available, corresponding to the different groups of domains described above.

Each API instance provides access to a set of domains (both XDDS and MR) depending on the characteristics of the requests.  Each instance is accessed using its own set of URL's for synchronous and asynchronous processing.

Important Note: As with any URL, these addresses are subject to change, so you should verify the addresses before using them.  Also, be sure to use the correct set of credentials for each of the instances.

The following table provides the URL’s for the different sets of domains.

Domain Set