Harrier, Isode's Messaging client, provides a modern user-interface to secure messaging on Web and Android platforms. Although initially targetted at the military market, Harrier has been designed for use in all sectors with strong messaging security requirements, in particular those needing support for security labels with messaging.

Developed from the ground-up with the needs of secure messaging users in mind, Harrier uses the Internet Standard SMTP (Simple Mail Transfer Protocol) for message submission and IMAP (Internet Message Access Protocol) for message and folder access, supporting a number of extensions for military messaging discussed in [Military Messaging (MMHS) over SMTP].

Harrier Web Server is a multi-threaded server process that runs on supported Isode server platforms and is distributed as an Isode server product. It supports multiple Harrier Web Clients, and connects using IMAP and SMTP to M-Box and M-Switch (or another server such as Microsoft Exchange).

Harrier Web Client is a JavaScript application that runs in the user’s Web browser, and will be downloaded as and when needed. Harrier Web Client connects using HTTP (REST) and Web Sockets to Harrier Web Server, making use of JSON, CSS, and HTML.

Isode server products provide seamless gateway access to/from message systems using SMTP and X.400 as well as military protocols such as STANAG 4406, ACP127 and constrained bandwdith variations.


Harrier supports a number of capabilites which make it ideal for use in secure environments including:

Security Labels

Support for Security Labels is based on RFC 7444 "Security Labels in Internet Email".  Isode's Security Label Server is used as the interface to enable Harrier to select a security label appropriate for the selected recipients. This client/server architecture, which allows flexible security labels to be provided without heavyweight client support, is described in detail in the whitepaper [Easy Security Label Support for Email Clients] .

TLS (Transport Layer Security)

TLS is important to provide data confidentiality. Harrier supports this for all connections, and account setup defaults to use of TLS, so that not using TLS needs to be a specific user choice. Harrier verifies server digital certificates against client trust anchors. Where a certificate is not correctly trusted, the user will need to confirm certificate use prior to use of the connection.

Time-Related Control Capabilities

Harrier allows users to set time-related controls. The reply by, expires on and deliver by controls allow the prioritization of messages handling. This capability is useful for time critical messages being sent over less reliable networks.

Draft and Release

A detailed description of this important military messaging capability can be found in the whitepaper [Open Online Draft & Release].

SICs and Message Type

Subject Indicator Codes (SICs) and Message Type are widely used military messaging fields. Harrier can set and display these. The values used are stored in the Security Label Server, so values can be managed centrally and shared between clients.

More information on the current and upcoming features of Harrier can be found in the [Harrier: Military Messaging for Web and Android] whitepaper.


Harrier is available for evaluation together with Isode's server products for Military Messaging. Please contact us using the Evaluation Request form.