Isode provides email server, gateway and client products for military messaging using STANAG 4406, ACP127 and SMTP protocols, including gateways between these protocols following ACP145 and MIXER. Isode products are ideal for deployment in both standard and constrained bandwidth environments.

What Isode Provides

Isode provides clients, gateways and servers for deployment as part of a military email solution:

  • ACP127: M-Switch products provide full support for ACP127 and related protocols, including ACP126, ACP128, JANAP128 and DOI103S.something about BRASS.
  • STANAG 4406: Isode's M-Switch X.400 includes full support for STANAG 4406 (including Annex E for Constrained Network Environments) and,
  • ACP145: Isode M-Switch MIXER can, together with M-Vault (an ACP133 military directory) be configured as an ACP145 Gateway to convert between national variants of S4406.
  • MMHS over SMTP: M-Switch SMTP can provide full military messaging capabilities over the industry standard STMP msail protocol.
  • Email Client: Isode's Harrier web based military email clients is a modern interface to military messaging compatible with Isode's server products and Microsoft Exchange.
  • STANAG 5066 Server: Isode's Icon-5066 is a modem-independent STANAG 5066 server. It enables applications to work efficiently over HF Modems/Radios and to allow multiple applications to work simultaneously.

All Isode Email Server products can be deployed as a Local MTA providing one or more of Isode's supported protocols or as a gateway between any of the listed protocols as well as SMTP and X.400.

Products are additionally optimised for operation in Constrained Network Environments including support for S4406 Annex E and ACP127 BRASS (Broadcast and Ship to Shore) deployments. Isode’s M-Switch SMTP and M-Switch MIXER also support CFTP (sometimes known as Battle Force Email/BFEM) for simple support of informal SMTP messaging for HF.


ACP127 is a text based protocol for formal military messaging. M-Switch provides full server side support for ACP127 and related military protocols, including ACP126, ACP128, JANAP128 and DOI103S. This includes gateway capabilities to SMTP and STANAG 4406. Isode also provides full support for operation over HF Radio and in particular for BRASS (Broadcast and Ship to Shore) deployments. More details can be found on the M-Switch ACP127 add-on page.


STANAG 4406 is the NATO Standard for formal military messaging. Used for both Strategic and Tactical messaging, STANAG 4406 has a number of special protocols to support tactical messaging, in particular to support very low bandwidth links such as HF radio (STANAG 4406 Annex E) and to support receivers in Emission Control (EMCON) mode who can receive but not send data.

Isode's M-Switch X.400 is fully compliant to the STANAG 4406 standards and architecture and can additionally be configured as a gateway to all other messaging standards supported by M-Switch X.400 and M-Switch STMP. More details can be found on the M-Switch S4406 Military Messaging page.


National variants of military messaging protocols have led to a situation where interoperability between national MMHS systems is not guaranteed. ACP145 has been defined in order to overcome this problem, and is a complete protocol definition for international inter-working. The ACP145 specification has led to a requirement for "ACP145 gateways", which convert between the national variants of MMHS and ACP145. M-Switch MIXER, alongside M-Vault (an ACP133 Military Directory) can be deployed as an ACP145 Gateway, and including support for Security Labels and Message Digital Signatures.

Use of M-Switch MIXER also enables national networks using SMTP and S/MIME to be connected using ACP145. Further details can be found in the Isode whitepaper [ACP145: Isode Support of International MMHS Gateways].


Full military messaging can be provided over the widely used and industry standard SMTP (Simple Mail Transfer Protocol) protocol. SMTP infrastructure can be shared between MMHS and informal email, reducing management overheads and to support communities where only partial MMHS capability may be required, or communities where a small subset of users require MMHS capability, without the requirement of deploying a separate MMHS infrastructure.

M-Switch SMTP features support for the wide range of Open Standards necessary to deliver military messaging over SMTP, including:

  • RFC 6710: SMTP Extension for Message Priorities
  • RFC 6477: Registration of MMHS Header fields for use in Internet Mail
  • RFC 7444: Security Labels in Internet Mail

This is described in the whitepaper [Military Messaging (MMHS) over SMTP].

Harrier Email Client

Harrier is Isode's web based military messaging client. Developed from the ground up with the needs of military messaging in mind, Harrier brings a modern user interface to military messaging and can be deployed as part of a solution using any of the messaging protocols supported by Isode's M-Switch familiy of MTAs and Gateways.

Harrier includes support for a number of key features that make it ideal for use in a military environment, including Security Labels, Time-Related Controls, SICs and Message Types. More information on Harrier can be found on the Harrier product page.

STANAG 5066 Server

Isode's Icon-5066 is a modem-independent STANAG 5066 server. STANAG 5066 provides a link layer optimized for HF Radio and described in the whitepaper [STANAG 5066: The Standard for Data Applications over HF Radio].

Icon-5066 can be configured with either one or two modems (one for transmission, one for reception) either through a crypto box or directly. Communication with each modem uses two independent channels; Data (mandatory) and Control (optional) and can be via synchronous serial, asynchronous serial or TCP (using MIL-STD-188-110C Appendix A).

Constrained Network Environments

Isode messaging server and gateway products can be configured for use over radio and satellite networks. Isode's core approach is to provide server-to-server communication, as this enables maximum efficiency to be obtained from the underlying networks, and isolates clients from those underlying networks. This allows use of standard clients, as specialized functionality is provided by the servers. Clients can connect directly to the Isode servers, or indirectly via other servers.

For more information see the M-Switch Constrained Networks product page.