Isode provides messaging server and client products for military messaging using STANAG 4406, ACP127 and SMTP protocols, including gateways between these protocols following ACP145 and MIXER. Isode provides Web and Android military messaging clients. Isode products are ideal for deployment in both standard and constrained bandwidth environments. On this page we look at Isode products for military email solutions, please see the page on Military XMPP for military instant messaging and multi-user chat.

What Isode Provides

Isode provides clients and servers for military messaging, deployed in a range of environments:

  • Isode's M-Switch MTA can be deployed to support STANAG 4406 military messaging (based on X.400), the older ACP127 protocol and military messaging over SMTP.
  • M-Switch provides gateway mappings between all the supported protocols, including MIXER.

Isode products feature support for message precedence, digital signatures using S/MIME for SMTP messages and STANAG 4406 ed2 signatures, security labels and security label mapping, message tracking for reliable messaging and operation over constrained bandwidth networks.

Military Messaging using STANAG 4406 (& STANAG 4406 Annex E)

STANAG 4406 is the NATO Standard for formal military messaging, replacing the older ACP127 specification. 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 is a market leading provider of STANAG 4406 messaging infrastructure. Details are given in the STANAG 4406 Military Messaging solutions page, including gateways to SMTP and ACP127.


ACP127 and related protocols are an older approach to text based military messaging, which are still widely used. M-Switch provides full server side support for ACP127 and related military protocols, including ACP126, ACP128 and JANAP128. 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 described in the whitepaper [Isode's Solution for BRASS].

Military Messaging over SMTP

Full military messaging can be provided over the industry standard SMTP (Simple Mail Transfer Protocol) family. This is described in the whitepaper [Military Messaging (MMHS) over SMTP] and RFC 6477 defines fourteen message headers, such as "MMHS-Primary-Precedence:" to extend a standard SMTP message. RFC 7444 defines use of security labels and RFC 6710 defines precedence handling. These extensions are supported by M-Switch.

Military Messaging Clients

Isode provides the Harrier family of military messaging clients, supporting full military messaging over SMTP, which can be converted to ACP 127 and STANAG 4406 by M-Switch. The lead product is Harrier Web, which provides an end user Web interface to military messaging. A mobile version of Harrier is provided on Android.

Instant Messaging and Multi-User Chat using XMPP

STANAG 4406 and SMTP are standards for store and forward messaging (email). Military communication is making increased use of real time (instant) messaging, both 1:1 and multi-user chat. XMPP is the Internet Standard for real time messaging and presence, and is gaining increasing military usage.

Isode M-Link XMPP server is available for both standard XMPP communications and, using an Optimized Server-to-Server protocol, for XMPP over low bandwidth links including HF Radio. MLink provides control of messages using security labels associated with the messages the security clearances of the users.

For further information see Isode's Military XMPP Solutions page.

Gateways with STANAG 4406

M-Switch provides conversion between all of the supported protocols, in particular:

  1. M-Switch MIXER provides a gateway between SMTP and standard STANAG 4406.
  2. A full ACP145 gateway, which provides STANAG 4406 edition 2 digital signatures and security labels and is designed to interconnect national military networks operating according to different profiles. For further details see the whitepaper [ACP145: Isode Support of International MMHS Gateways].
  3. Gateways between ACP 127 and SMTP and/or STANAG 4406.

STANAG 4406 gateways are discussed in more detail on the STANAG 4406 Military Messaging page.

Applications for Military Radio & Satellite

Many Isode applications are optimized for use over Radio, Satellite and other multicast and potentially low quality/performance links. Although this functionality may have general application, Military organizations are the primary target of these applications, and a number of protocols specified for military use are key to Isode's product set.

Our Applications for Military Radio & Satellite solutions page gives an overview of the products and management tools that Isode provides for Radio and Satellite networks, giving a communication network oriented view of the Isode product set.


Message precedence is critical for military operations over slower networks. Isode M-Switch supports this, with controlled grade of delivery for the six military precedence values. It also supports MINIMIZE, so that processing of lower precedence messages can be suspended. This capability can be controlled by clients using the MMHS-Primary-Precedence header. MSwitch also supports SMTP priority following RFC 6710 "Simple Mail Transfer Protocol extension for Message Priorities".

Digital Signatures

Isode supports digital signatures of messages using S/MIME for SMTP messages and STANAG 4406 ed2 signatures. M-Switch can verify message signatures, strip message signatures, and add signatures to messages. This provides high flexibility for digital signature use in environments with mixed capabilities and protocols.

Security Labels

Isode provides comprehensive support for Security Labels and Security label mapping in M-Switch. For information on M-Switch use of security labels see the M-Switch product page. For information on Isode general security label capability see the Isode Security Policy, Security Label and Security Clearance Infrastructure & Management product page.

Tracking and "Fire and Forget"

To provide reliable messaging, delivery reports and read receipts can be used. These enable message tracking to record problems and to detect when messages are delayed. This can be monitored by Isode MConsole.

This capability can be used to provide a "fire and forget" capability, where the message sender can be confident that once a message is sent that it will be delivered and acted on, which is vital when messaging is used for command and control. For further information see the whitepaper [Using Message Acknowledgements for Tracking, Correlation and Fire & Forget].

Constrained Bandwidth

Operation over constrained networks is vital for many military deployments. Isode offers a SMTP messaging solution based on the ACP 142 military specification. This provides optimized communication for both point to point and multicast networks, and operation in EMCON (Emission Control or Radio Silence). This can be operated over IP networks such as Satcom and fast radio links. Isode also supports direct operation of STANAG 5066 to give optimal performance for HF Radio.

For more details on protocol stacks, M-Switch operation over constrained networks and a list of relevant whitepapers see the M-Switch: Constrained Networks & HF Radios product page and the [Isode's Solution for BRASS] whitepaper.

Further information

Isode whitepapers on this subject can be found from our whitepaper section on Military Messaging, including:

  • Using Message Acknowledgements for Tracking, Correlation and Fire & Forget
    This whitepaper looks at how tracking end to end message acknowledgements can improve service reliability for mission critical messaging. This is achieved by enhancing message tracking services and providing information on messages being delivered and read. It then describes how this can be extended to provide a "Fire and Forget" quality service, using operator alerts and guaranteed action points (GAP). The paper also shows how these capabilities are provided in Isode's M-Switch product.
  • Military Messaging (MMHS) over SMTP
    Military Message Handling (MMHS) is specified in STANAG 4406, which operates over the X.400 Messaging protocols. This whitepaper looks at how MMHS could be provided over SMTP noting where this can be done with existing standards, where there is active work to define standards, and where there are currently no standards. It concludes with a summary of what is needed to make MMHS over SMTP a reality that can meet operational requirements.
  • The Architecture of Isode's STANAG 4406 Annex E Solution
    Military Messages often need to be transferred over low bandwidth networks, in particular HF Radio and Satellite Networks. Isode provides ACP 142 and STANAG 4406 Annex E as a part of its M-Switch X.400 product. This paper describes Isode's approach to implementing these protocols, and how this addresses basic and advanced operational problems, management approaches and integration with other components as part of a larger solution.
  • Isode's Solution for BRASS (Broadcast and Ship to Shore)
    BRASS (Broadcast and Ship to Shore) is an approach used by Navies, particularly in NATO countries, to communicate between Ships and Shore using HF Radio. This whitepaper gives an overview of BRASS and then describes the Isode strategy and solution for this area. It looks at how Isode’s products can support the protocols and interoperability for currently deployed BRASS systems and move them forward to state of the art capabilities that extend the services offered over BRASS.