M-Box Gateway enables mail clients to indirectly access one or more back-end servers. Client/Gateway protocol and Gateway/Back-end Server can use either Internet Standard POP (Post Office Protocol) or IMAP (Internet Message Access Protocol). M-Box Gateway is based on M-Box, Isode's IMAP and POP message store.

M-Box Gateway can operate as 'pure gateway' as shown below, where all messages are delivered to back-end servers, and M-Box gateway simply provides the protocol and service mapping. M-Box Gateway can also operate as an M-Box server, with a local mailbox associated with each user.

The back-end of the M-Box Gateway accesses one or more POP or IMAP servers. The front end of the gateway is identical to that of M-Box and provides an IMAP and POP interface to clients. Messages are stored by the M-Box Gateway to optimize access performance for an IMAP client. Operation is as follows:

  1. When a Client connects, the back-end of the M-Box Gateway connects to the back-end POP or IMAP server and downloads a copy of all messages (messages are left on the back-end server and are deleted only if the client deletes the message on the frontend. Both servers remain in sync)
  2. M-Box Gateway is now in a position to provide IMAP or POP access to those messages from IMAP or POP capable clients.
  3. While an IMAP or POP connection remains open, the M-Box Gateway back-end will poll the back-end servers (at configurable intervals) to retrieve new messages.
  4. The M-Box Gateway can notify the IMAP client when new email messages arrive using the IMAP IDLE command.
  5. Continued Synchronization between the Gateway and the backend POP servers means that messages marked for deletion 'on the server' are deleted from both the Gateway and the backend POP server.
A key benefit of this architecture is that back-end servers are only accessed when clients are online. This is an important performance optimization in many situations, where accounts are idle or only accessed for a fraction of the time.


M-Box gateway provides two modes of authentication The first is to use the back-end server for authentication. Here authentication information provided by the client is passed to the back-end server. This approach leads to a very simple configuration, which can be helpful for some deployments.The second model is to use authentication information configured in an LDAP directory as shown below. The Directory will be used for:
  1. Authentication of the client connecting to M-Box Gateway.
  2. Authentication for each of the back-end servers, with the directory holding configuration and authentication information for each back-end account.

Folder Model

M-Box gateway has two models for inbox representation. The first model is to have a single inbox, with all back-end accounts synchronized to that inbox. This gives a simple model for IMAP clients, and one that will work for POP clients.The second model is to have a special (sub) folder for each of the back-end servers. This model will give a more flexible approach for IMAP clients.

Deployment Targets

M-Box Gateway is primarily intended for use by service providers providing a mobile or IMAP email service. There are four deployment models, described below.

Deployment Model 1: Mobile Users with POP-only accounts

POP is the most widely used open standard message access protocol, and many users have mailboxes which only support POP access. POP is not an efficient access protocol in situations where slow and/or expensive network connections are used (as in access over a mobile network as illustrated by our whitepaper on [Accessing POP servers from mobile devices]). The M-Box Gateway allows users to access their POP mailboxes using the more efficient IMAP protocol and be notified of the arrival of new messages using the IMAP IDLE command without having to initiate a check for new messages as would be the case with POP.

Deployment Model 2: LEMONADE Clients without LEMONADE servers

LEMONADE is the open standard for Mobile messaging. It has a client/server architecture and can operate directly to the user’s mail server. However, in many cases the server will not support IMAP or will support IMAP, but not the LEMONADE extensions. Most mail servers support POP3 access. Because of this, M-Box Gateway can be used as a general purpose LEMONADE gateway to any email server.

Deployment Model 3: Mailbox Consolidation

Users will often have multiple mailboxes. Configuring a mobile device to access every account can be a significant overhead. M-Box gateway can provide integrated access to multiple mailboxes.

Deployment Model 4: Service Provider External Mailbox Support

A service provider may use M-Box to provide a mailbox server. M-Box Gateway allows this service to be extended to integrate in multiple back-end mailboxes, and to bring all of the user’s mail under integrated control.

Configuration Management

Configuration management is done using the Web interface provided by Isode's Internet Messaging Administrator (IMA).

Operational Management

M-Box Gateway has the same operational management capabilities as M-Box, including SNMP monitoring of gateway status and both IMAP and POP connections.

Internet Mail Conformance

See the M-Box product page for conformance information.