Component architecture

While grommunio is distributed as appliances, grommunio is also available as packaged software. The packaging is oriented on the modular component structure of the software modules available by grommunio. The modular component layout of grommunio allows a component-based deployment for all sorts of deployments and operations - ranging from single deployments with high-density component layout to scale-out, distributed component layout.

Architecture of grommunio components

The grommunio component layout supports a wide range of deployment types:

  • Containers (Docker, LXC)

  • Virtual machines (KVM, VMware, Hyper-V)

The appliances shipped by grommunio contain all components required for operation by the use of packages which are available for updates via repositories. The appliances ship these packages as part of the appliance distribution to be able to operate the installation without external repository activation necessary (whilst deploying with active internet connection for updates at deployment is strongly encouraged).

To understand the component architecture and the interconnectivity of these components, the following chapters show the single components and how they interoperate with other components in the entire component stack.

Protocol / Component Flow

grommunio is a comprehensive communication and collaboration solution that covers and delivers protocols with a vast variety of computer standards for communication. The main protocols delivered by grommunio are:

Wire-level protocols:

  • SMTP

  • IMAP

  • POP3

Application-level protocols (HTTP-based):

  • RPC/HTTP (OutlookAnywhere)


  • EWS (Exchange Web Services)

  • EAS (Exchange ActiveSync)

  • CalDAV

  • CardDAV

With these numerous protocols available, grommunio needs to have an effictient component flow. Since protocols may be accessed in parallel for the same dataset, grommunio takes care of parallelization and protocol tracking. To ensure operation, security and functionality, grommunio uses a set of different components as well as a plugin-based structure for larger components. This way, components may be extended for future feature expansion and allows nearly-realtime patches and updates. More complex setups gain from the component/plugin architecture as the scalability of the components allow various flavors of containerization and orchestration.

The following illustration shows the combined protocol and component flow for grommunio Groupware based components:

Protocol and component flow of grommunio Groupware


SMTP is the main protocol used for mail transport. For illustration purposes, there is a distinction made of the internal mail flow as well as external mail flow.

The entire transport is configured to be gapless in terms of email processing. This way, grommunio protects also from internal outbreaks (for example spam or virus distribution).

The configuration outlined here defines the default configuration set. In many cases, even more sophisticated setups might be envisioned, as with extended integration of security appliances. The following workflows provide the process definition which provides a view to where a preferred hook might be implemented.


SMTP workflow of incoming mails

Mails are processed as follows (applies to incoming and outgoing):

  1. The included Postfix MTA receives messages and passes them to grommunio-antispam via the Milter mail filter protocol.

  2. grommunio-antispam checks the message for spam. If configured, grommunio-antispam (optionally) passes the message to an anti-virus processing service.

  3. The response from the anti-virus check is read back by antispam.

  4. The response from antispam is read back by Postfix.

  5. Postfix evaluates the contents of the Envelope-From and Envelope-To address pair to make the decision if this is i incoming or outgoing mail.

  6. Incoming mail is relayed to the gromox-delivery process, which converts the mail to a MAPI object and places it in the user’s mailbox.

  7. Outgoing mail is delivered to a configured relayhost or to the next MX destination that is responsible for the target address.

SMTP workflow of outgoing mails


RPC & EWS workflow

The main protocols used by grommunio for MAPI-based connectivity - as used for example with Microsoft Outlook - are:

  • RPC/HTTP (OutlookAnywhere)


  • EWS (Exchange Web Services)

All of these protocols are HTTP-based which is why these are routed through the shipped nginx web server, primarily for security, scalability and monitoring reasons.

MAPI-based connections are processed as follows:

  1. In the first stage, the endpoint utilizes AutoDiscover ( technology (with Authentication) to discover which service endpoint URL is responsible for it.

  2. If the AutoDiscover endpoint ends up at the same service (If not, it will be redirected to the other endpoint URL), nginx routes the connection directly to the gromox-http service which handles the connection.

  3. For access to the users’ mailbox, gromox-http’s emsmdb plugin connects to the exmdb plugin for mailbox data delivery.

Exchange ActiveSync (EAS)

Exchange ActiveSync (EAS) workflow

The main protocol used for mobile devices and tablets is Exchange ActiveSync (EAS). EAS is a synchronization state-based protocol which uses state data to determine its current synchronization status. EAS is often synonymously refered to as “Push Mail”, since it is permanently connected to its service and listening for updates. As such, EAS is recommended as protocol for mobile devices especially over unreliable networks, such as cellular networks. While it is possible to connect certain clients, including Microsoft Mail and Microsoft Outlook, it is strongly discouraged to do so. Compared to its more performing alternatives, such as MAPI/HTTP, the EAS protocol is slower for bulk data transfer or large to very large (10 GB+) mailboxes. At last, the EAS protocol only delivers a subset of features available to other protocols.

EAS-based connections are processed as follows:

  1. In the first stage, the endpoint utilizes AutoDiscover ( technology (with Authentication) to discover which service endpoint URL is responsible for it.

  2. If the AutoDiscover endpoint ends up at the same service (If not, it will be redirected to the other endpoint URL), nginx routes the connection to grommunio-sync which natively provides the /Microsoft-Server-ActiveSync endpoint to its device.

  3. For access to the users’ mailbox, grommunio-sync connects to gromox-zcore which delivers PHP-MAPI interfaces to access

  4. gromox-http via exmdb plugin for mailbox data delivery.


IMAP workflow

IMAP workflow


POP3 workflow

POP3 workflow


Authentication workflow

Authentication workflow